Microsoft does many things wrong, but one thing it does very well is long-term support for its products. As a case in point, Windows for Workgroups, born to the world in 1993, is finally being retired on November 1, 2008. Fifteen years...Most software companies haven't even been in existence that long.
The only way that open source can replicate this, given commercial open source's young age, is through "perpetual escrow." Even so, if I'm an IT buyer it matters to me that Microsoft, IBM, etc. have been around a long time, and will be around for an even longer time.
Now if I could just get vendor longevity and open source at the same time, in the same place, I'd be golden.