It's a UNIX box, man. The most
(programmer-)friendly OS in
existence. At least for even moderately technical people.
There are
UNIX-compatible people and non-UNIX-compatible people (cf
Unix Hater's Handbook).
Even aside from that, I'm not convinced. I think Symbolics Genera is
arguably more programmer-friendly, though that could just be because I
find Lisp a much nicer language than C. (There may be even better
OSes; that's just what I have personal experience with.)
I find programming under batch-mode OS to be more pleasurable.
Peace... Sridhar