Not such a no-brainer for some. Although savings may come in the long run with OSS, it costs money for most businesses to migrate platforms no matter what they're coming from or going to. With a recession, they might be more worried about spending the money they have right now rather than long-term savings.
Microsoft has been imposing significant migration expenses because of unnecessary changes between software versions.
It’s probably easier and cheaper to migrate from Office 2003 to OpenOffice.org than it is to migrate to Office 2007.