Microsoft has used GDC to announce the launch of its XNA platform, advertised by the colossus as "a powerful next-generation software development platform." For any one who knows Microsoft however, it is clear that things are not as straightforward. XNA will cover games for future iterations of all Microsoft game platforms, including Windows, Xbox and XBox 2 and Windows Mobile, based devices. As is the case with most all-in-one systems it promises to free developers from spending too much time …