It does go a bit deeper than not trusting folks[1]. Sometimes you must make sure you comply with information sharing laws in your field (e.g. HIPA). Two, most people are not super computer literate and just want the damn thing to work. Having a standard config that you slap down with their data stored on good servers is actually a pretty helpful thing to them. They don't want control of their machine, they want stability, reliability, and recovery from mistakes. The accountant wants to do his/her job and not learn IT's job.

As much as I'm not a fan of Windows Servers, I understand that they provide a pretty easy, integrated approach. I do wish open source projects would look to that and not think what's available is good enough. People will trade up their Camry for a Lexus, but not willing trade down to a Yaris.

1) although with over 1,000 or 10,000 employees you probably should assume you've hired some damn fools or evil folks - that's just basic numbers