Apple’s U.S. MacBook sales came in softer than expected in December, according to NPD

MacBook Air. Photo: Apple Inc.

In a note to clients issued Tuesday, Piper Jaffray’s Gene Munster offered his analysis of the NPD Group’s final PC retail sales data for 2011.

The news, as he sees is, is good and bad.

Domestic Mac unit sales were up 12% for the quarter, according to NPD, which isn’t bad given that sales of Microsoft MSFT Windows PCs are shrinking.

But the Street was expecting Mac sales for December to be up 25%. Accordingly, Munster is shaving 300,000 units off his Mac estimate for fiscal Q1 2012, dropping it to 4.9 million from 5.2 million.

But at the same time, he’s raising his iPhone sales estimate by 600,000 units — to 30.6 million from 30 million.

The result, Munster says, is a wash for Apple AAPL . His top and bottom lines remain unchanged: He expects the company to report earnings next week of  $10.50 on sales of $40.187 billion.

See also: By how many billions is Wall Street low-balling Apple?