Apple bucked the U.S. trend last quarter by posting double-digit Mac sales gains. Still, the Mac dropped to the fifth spot in U.S. computer sales during the final quarter of 2010 as strong sales to businesses by rivals pushed it two places down the list.

Both IDC and Gartner had Apple in the No. 5 position for the fourth quarter, behind Hewlett-Packard, Dell, Acer and Toshiba. According to the IDC research group, Apple sold over 6.5 million Macs in the US in fiscal year 2010 for 8.8% market share. The compares to over 5.6 million Mac shipments in 2009 for 7.8% market share — a growth of 18.4%.

According to Gartner, Apple sold 1.9 million Mac desktops and laptops during the fourth quarter to snare 9.7% of the U.S. market. IDC listed U.S. Mac sales at 1.7 million, giving Apple an 8.7% share. Apple beat the U.S. industry average growth rate by huge margins. Only once since 2003 has the Mac not grown in year-over-year sales faster than the industry average. For the latest quarter, of the top five U.S. computer sellers, only Apple and Toshiba posted postitive year-on-year gains.

However — and this is important — if you counted the iPad as a computer — which I think you should — Apple’s ranking would be substantially higher. As noted as “Computerworld” (http://macte.ch/CJRQy), Gartner and IDC separate tablet sales from personal computer numbers, but if they put the iPad in the computer spot — as they do netbooks, for instance — Apple would likely have captured the world’s No. 3 spot.

Counting only Mac sales, the company doesn’t quite rank among the top five global computer makers. Should tablets should be considered part of the personal computer market, Appleā€™s worldwide computer market share would rise to 12% this fiscal year, from 4.4% at present.

Other analysts, like Brian Marshall of Gleacher & Co., have estimated worldwide iPad sales in the fourth quarter at six million, Mac sales during the same period at over four million. The total of 10 million would move Apple up to third place in IDC’s global top five, behind only HP and Dell. The same 10 million would put Apple in fourth place on Gartner’s list, notes “Computerworld.”

“The US market was expected to shrink year over year given the exploding growth experienced in the fourth quarter of 2009,” says David Daoud, research director, US Quarterly PC Tracker and Personal Computing. “Growth steadily slowed throughout 2010 as weakening demand and competition from the Apple iPad constrained computer shipments. In addition to relatively high market penetration and a ‘good-enough’ computing experience with existing computers, consumers are being more cautious with their purchases and competing devices have been vying for consumer dollars. This situation is likely to persist in 2011, if not worsen, as a wave of Media Tablets could put a dent in the traditional PC market.”

Jay Chou, research analyst, Worldwide Quarterly PC Tracker, adds: “Consumer fatigue is playing an important role in many markets as the Mini Notebook surge wanes and consumers watch their spending and evaluate other products. Softening demand in Asia/Pacific and the potential for similar changes in other regions represent the biggest potential shift in personal computer growth during 2011. These factors are likely to slightly reduce growth from previous projections of about 10% for 2011, although replacements in the commercial segment and aggressive competition should still support double-digit growth in the second half of the year.”

— Dennis Sellers