In the face of NPD results for December 2009, Microsoft has today chosen to focus on its yearlong results and historical performance, highlighting a worldwide install base of 39 million Xbox 360s and a software tie ration of 8.8 games per console sold.

Truth be told, Microsoft’s performance in December last year wasn’t all that bad, with 1.31 million Xbox 360s finding their way into American households (earning it third place in the home console race) and three Xbox 360 games on the top ten software sales list (with just over 3 million units sold between them) as opposed to the PlayStation 3’s single title.

Microsoft noted that the Xbox 360 sold 10 million units in the US during 2009, while the system generated $4.8 billion in revenue, which is down from $5.0 billion in 2008 and $5.1 billion in 2007.

Third-party software developers must be smiling though, as this class of game generated $2.4 billion in revenue over the year on the Xbox 360, representing 43% of the industry’s third-party game revenues for 2009.

Microsoft’s online service, Xbox LIVE, also broke a few records and saw its highest concurrent number of users in 2009, with 2.2 million people online at the same time.

Looking to the future (or the present, as you like) instead of the past, Microsoft pointed to the releases of Splinter Cell: Conviction, Mass Effect 2, Halo Reach and Project Natal to contribute to what the company believes will be the Xbox brand’s “biggest and best year” ever.

See what Nintendo and Sony have to say about the December’s NPD results, and read about the overall performance of the US retail console game market in 2009 over here.