It's been a while since I used a Linux laptop (I was a Linux on laptop
& desktop full-time user for 5+ years) but certainly one of the big
draws for me in Mac/OS X has simply been the *feel*. The fonts look
great (useful when you're reading them 10+hours/day): they're typeset
well, antialiased well, crisp, attractive. The Retina display is
amazing. It's obvious folks with serious design chops are behind it
all. For me, Linux & Windows have always felt clunky in comparison.
If you want to get a deep sense of this, watch
http://www.helveticafilm.com - there is a hilarious & epic
anti-Microsoft rant by Erik Spiekermann about how Arial was a rip-off
of Helvetica for MS to avoid having to pay Linotype,
http://www.youtube.com/watch?feature=player_detailpage&v=F691weEVpwc#t=291
Macs... A lot of stuff Just Works(tm): multi monitor, devices, swipe,
etc. If I could monetize the time I spent fiddling with xf86config
over the years I'd likely have paid for every Mac I've owned. (I'm
sure it's better now?).
For me, having a machine that wakes from sleep nearly instantly, has
reliable trackpad + gestures, consistent copy/paste behavior, and so
on, is worth the money.
Finally, there's the development environment - this is the massively
personal choice that is likely the big decision maker for most.
There's no point justifying what each person likes any more than their
taste in broccoli but ultimately if you really like OS X or Linux,
well... :)
Paul