Like ron said, i too can see open source options being more used in the future once the knowledge is out there but right now I think companies are cautious to turn to the open source route because it could hurt them if they do it wrong and it could cost them a lot of money up front to train employees on it, find people that have experience with it, time lost from issues, etc..

I work for a contract programming company and our business is booming right now because companies save lots of money by not having to hire and train employees with benefits and my company already has the software and hardware in place to do what our clients need and we are 100% MS with no thought of changing (that i know of). Mainly because MS gives us so much free stuff. I am currently the only programmer that has experience with PHP for the few clients that actually need it.

Actually, now that i think of it. One of our competitors hired us to finish a project for them for a large company (fortune 50) that was all in PHP and hosted on a linux server. I never got to find out if the server was at the clients or the people that hired us to finish it but my guess is that it was our competitors choice on linux and not the client but i could be wrong.