With less than two weeks before the end of Apple’s March quarter, Shaw Wu of American Technology Research expects the company to shake off the doldrums that are dragging down the rest of the U.S. economy.

“Our sense is that the Mac business is recession proof,” he writes in a report to clients issued Thursday morning. Based on his supply chain checks, Wu sees good news throughout Apple’s (AAPL) product line:

• Rather than the 38 percent year-to-year growth in Macintosh unit sales he had earlier predicted, he now thinks growth may be closer to 42 percent.
• After a strong start and then a lull, he sees Macbook Air sales picking up rapidly. “Customers are attracted to its super thin form factor and do not seem to mind some of its limitations.”
• He’s seeing a bump in iPod sales following the shuffle price cut, and now expects iPods to come in at the high end of his 9.5-10 million unit range (but lower than the Street’s 10.8 consensus).
• He sees a pause in iPhone sales following the well-regarded SDK announcement as customers wait for the June release of iPhone 2.0. He’s modeling 11 million iPhones for the year, slightly ahead of Apple’s 10 million target.
• Falling prices in component parts should sweeten Apple’s March report, due out April 23, and Wu is raising his estimates accordingly. He writes: “For the March quarter, we are now modeling $7 billion and $1.10 in EPS (from $6.9 billion and $1.02) vs. consensus of $6.92 billion and $1.05 and its guidance of $6.8 billion and $0.94.”

A lot has been written about Dell’s third-quarter earnings report, but what caught the eye of analyst Shaw Wu of American Technology Research was its disappointing gross margin: 18.5%, down 150 basis points from 20% a year earlier.

“Controversial and confusing,” Wu called Dell’s (DELL) explanation for these results, especially in comparison to competitors like Apple (AAPL) and Hewlett Packard (HPQ).

“DELL cited a tougher component pricing environment. We find this odd as AAPL and HPQ experienced the opposite and our own supply chain checks indicate otherwise. … It is interesting to note that DELL’s costs may actually now be higher than HPQ and AAPL, something that was unthinkable not that long ago.”