OSX and android are the shame full special brother of any good *nix distribution... Android is Linux done wrong and OSX is freeBSD after a car crash and a rape... A big ugly shame if you ask me....
and I almost guaranty you that apple iOS on phone will be behind MS sooner or later... Looking at current trends in a big chunk of Europe it will be in the next few years...
and I still have my doubts on dumb tablet long lasting appeal... Once x86 processor and hybrid builds will be cheaper and less power hungry...
well anyway in the tech world things can always change radically within 10 years or stay stagnant for 20... Only time will tell us
but comparing OSX, android, iOS to linux/freeBSD is like comparing a Ferrari to a formula 1 not only they are not in the same ball park by a couple light years but if you somehow know how to handle one certainly don't guarantee that you'll appreciate the other one let alone manage to use it properly....
heck I'd wager that a bigger ratio of the MS OS user base would be comfortable on a true Linux/FBSD rig than apple or google regular users...
now that being said, I don't think steam OS will change anything...It will be a nice alternative to other Linux distribution more focused on games nothing more and nothing game changing for anyone no pun intended...
