Why does IBM embrace Open-Source

Much has been made by myself as well as others, about IBM’s open arm embrace of open source software. A great article at preens.com notes the oddity in the following way: IBM, the epitome of conservative business, de-emphasizes its billion-dollar “AIX” operating system in favor of a product developed by a loose coalition of programmers with no financial motive in common, upon whom no corporate directive can be binding, whose leader has no power but the respect of others.

Why does IBM embrace Open-Source.