In my experience dealing with boring corporations, that's another myth. Yes, they run Exchange. But all new developments I've seen happen on Linux boxes, precisely because it's easier to outsource IT.
Perhaps it depends on how boring/conservative the corporation is. At a past job where we worked with big banks, they'd sometimes look at you suspiciously if your application didn't run on Windows Server.
That's just anecdotal, though. Maybe we were just unlucky and worked with odd customers.
