The reason is obvious: These three companies dominate the smartphone industry with a shocking totality.
Google dominates mobile search revenue in part because of its Android platform and in part because of its iOS apps. Google made about $5.2 billion in mobile ad revenue last year worldwide and grabbed an incredible 93.3% share of the U.S. mobile search ad market.
The rest of the industry is fed up with watching Apple, Samsung and Google run away with all the money. Now they're fighting back.
The industry is competing again and they're doing it right -- with innovation, imagination, design and sound strategy.
Here's how each of the leaders was challenged in Barcelona this week.
Apple didn't have a booth, yet had a presence at MWC not unlike Lord Voldemort's in the Harry Potter series -- the scary, powerful entity that must not be named.
A general mob scene at the HTC booth involved long lines forming behind the dozens of tethered demo units of the recently announced HTC One phone. Many people were snapping pictures of the HTC One with their iPhones.
The HTC One is by far the most beautifully designed Android phone I've ever seen, with its elegant, unibody aluminum construction.
The HTC One challenges the iPhone on Apple's own terms -- with elegant hardware design, a fantastic camera and a compelling user interface.
Apple's monopoly on elegant hardware design is officially over.
An even bigger threat to Apple's dominance, however, is the general excitement over phones totally unlike iPhones.
The hottest thing in smartphones at the show was raw power: 13-megapixel cameras, blistering-fast mobile processors, giant screens, incredibly loud and clear speaker systems and surprising and innovative connectivity options to TVs and other devices.
The iPhone suddenly feels stale and feeble.
Samsung had an enormous booth, as usual, but didn't announce its upcoming Galaxy S4 phone, which will be unveiled March 14 in New York.
Samsung's new handset competitors are hitting the company with a combination of great design, compelling features and raw power.
LG demonstrated some surprising technology that I didn't think was even possible. They showed an LG Optimus G running a graphically intensive game mirrored over HDMI and upscaled to Ultra HD TV (also known as 4K) -- a TV technology so new that they're selling for around $20,000 per TV set. Hollywood isn't even producing much 4K content.
ZTE surprised the MWC crowd by announcing a phone called the Grand Memo running Qualcomm's Snapdragon 800 processor with LTE connectivity -- which can run at a clock speed of 2.3 GHz. (Note that Samsung's upcoming most-powerful phone, the Galaxy S4, will reportedly run the slower Snapdragon 600 in one model for the U.S., and a second version running Samsung's eight-core Exynos 5 Octa chip for the European market.)
In the wake of MWC, Samsung's design, performance and feature advantages on the high end of the market are seriously eroded.
But there's trouble on the low end, too.
For example, Nokia's Lumia 520 phone is a pretty advanced Windows Phone smartphone that should cost less than $185. Upstarts like Huawei and ZTE were showing low-end phones that provide most of the features and functions of high-end phones, but at very low prices.
These are the kinds of phones that are likely to chip away aggressively at Samsung's global market share.
Google decision to go boothless at MWC this year surprised attendees. Last year's Google booth was ginormous and their show presence overwhelming.
Google's Android platform is by far the world's biggest phone operating system. Devices running Android were everywhere at the show.
But there's trouble in paradise, and this was plain to see at MWC. The problem: The marginalization and commoditization of mobile operating systems in general and Android in particular.
On the one hand, some of the very best Android phones, such as the HTC One, are running proprietary user interfaces (like HTC's BlinkFeed, which is similar to Windows Phone 8's Live Tiles interface) and custom apps that define the experience of using the phone.
In general, the custom-built user interfaces created by handset makers are taking the experience further away from the Android experience and the Google revenue model.
One of those alternatives, the Tizen platform, under development by Samsung and Intel, looms large, as Samsung intends to use it to replace Android on some phones and become more like Apple -- a company that sells not only the hardware, but the software and gets a cut of all the downloads.
The threat to Google here is the marginalization and commoditization of the platform OS.
If consumers buy phones based on hardware plus bundled software created by the handset maker -- and if those handset makers do what Amazon does, and redirect buyers away from Google advertising and downloadable content toward their own -- then Google's mobile business will suffer.
Everybody wants a piece of Google's mobile revenue, and they'll go after it by either hijacking Google's own Android or replacing it with a competitor.
As Google loses mindshare, they'll lose market share. And as they lose market share, they'll lose revenue share.
It's easy to dismiss the new mobile platforms. After all, they can't hope to compete against Apple or Google for the quality and variety of apps in the app stores.
But one of the most promising platforms of the lot demonstrated at MWC, Ubuntu Touch, runs Ubuntu Desktop apps and can even be used as an Ubuntu Desktop PC when you connect the phone to a large, external display. And, in any event, it's easy for developers to port Android applications to run native on Ubuntu Touch.
But most importantly, these upstart mobile platforms won't come at Android on the high end of the market, but on the low end, where apps are far less important.
A phone on display at MWC called the ZTE Open running the Firefox OS can serve as the poster child for the insurrection against industry leaders. Here's a phone made by a company most Americans have never heard of, but which already sells more phones in China than Apple does. The phone isn't involved in any way with Apple, Google or Samsung, and challenges them all, at least theoretically.
MWC revealed a ubiquitous, industrywide strategy to chip away at the dominance of Apple, Samsung and Google with a two-pronged strategy.
First, thrill advanced users on the high end with mind-blowing processing power, advanced features and great design -- beat Apple and Samsung by going bigger and better on all components.
Second, thrill emerging and low-end markets with very low-cost phones and features using Android alternatives, gobbling up global market share.
Don't get me wrong: Apple, Samsung and Google will continue to be the smartphone industry's global leaders for the foreseeable future.
But when it comes to market share, revenue and profits, the industry giants must now learn how to share.
See more Mobile World Congress coverage from our team in Barcelona.
Mike Elgan writes about technology and tech culture. Contact and learn more about Mike at http://Google.me/+MikeElgan. You can also see more articles by Mike Elgan on Computerworld.com.
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This story, "Apple, Samsung and Google Under Fire at Mobile World Congress" was originally published by Computerworld.