[k7d]

Most enterprises have a very strong culture of maintaining status quo as extensively as possible. Especially in IT departments. Even big software enterprises rely on 5-10 year old infrastructure software (such as Exchange 2003) which was released during the era of Windows domination. It doesn't help that some of the software is web based because even that is often made for Internet Explorer only.

Nevertheless Mac's are actually spreading in enterprises. Not from top but from bottom. Officially unsupported, but with a help of VM software such as VMWare Fusion there are no problems using legacy stuff.