Earlier quoted context omitted.
My last couple of jobs have given me no choice aside from a MBP and OS X. They do this because they don't want to manage multiple kinds of machines from an IT perspective. (I'm not sure I agree with this, but it is what it is.) Depending on how widespread this is, usage may not reflect actual user desire (though I would wager quite a large number of users either don't care what they're using, or care, but a MBP is ad…
The managing multiple kinds of machines issues is a real one, speaking from the other end. For uniquely talented software engineers I might let them use what they want but from managing an IT department you definitely want anyone who has no reason to be otherwise on the same exact hardware and software configuration.
That feels like a fair solution.