Mac retail sales in the U.S. last month fell 1 percent from a year ago, even as sales of Windows PCs climbed 7 percent, market research company NPD Group Inc. reported today.

The downturn is a turnabout for Apple, which through October had managed to maintain growth significantly above the PC industry average, and—if followed by soft sales this month—could push the company to cut prices, said NPD analyst Stephen Baker.

"Apple's not immune to the economy," said Baker. "Nor is it immune to having an aged product line. The iMac is long in the tooth."

Buyers last month apparently agreed with that view. According to NPD Group's data, which includes sales results from both brick-and-mortar retailers as well as some of the larger online stores, such as Amazon.com, sales of Apple's desktop computers plunged 38 percent in November compared to the same month the year before. Sales of desktop PCs equipped with Windows also fell, but they were down just 15 percent.

"[Apple's] average desktop price is more than twice the industry average desktop price," said Baker, pointing out the relatively high prices for iMacs, which start at $1,199. "If you look at Apple's product line, and ask, 'Where is the hole?'—anybody will answer 'iMac,'" Baker added.

Apple's current iMac line is little changed from what the company rolled out in August 2007 when it last refreshed its desktops.

The bright spot for Apple was its laptops, which posted sales gains of 22 percent over November 2007, easily outpacing the 15 percentgrowth of Windows-based laptops.

"You never don't want to grow sales, but the thing to point out is that the models that generate 80 percent of Apple's volume, notebooks, were still growing 50 percent faster than the rest of the notebook market," Baker said.

Apple's share of retail laptop sales in the U.S. also dropped in November from the month before, slipping to 14.8 percent from October's 20.9 percent. NPD Group credited the mid-October debut of the newest MacBooks and MacBook Pros with that month's strong showing.

To some degree, Baker said, Apple was a victim of timing as well as its sales traditions. "Some of this was a result of the calendar," Baker said, noting that Black Friday—typically the day that Apple jump-starts sales with a one-day promotion— arrived on Nov. 28 this year. "It was the very last week of the month," Baker noted, "so there were very few holiday sales in the month for Apple."