This is what's keeping them from doing the same. They could always fork Android, but then you end up with Amazon Kindle Fire. Although... If the Ubuntu phones get anywhere it could be part of that ecosystem if Ubuntu makes it so, but who really knows at this point, it's too early to tell. It's much too complicated when Steam is it's own App market, and it would not provide much revenue for other companies, or incentives if you will?
There's the steam box I suppose. A steam handheld would be pretty cool. I love the 3DS, but it is underpowered and the games are hella expensive. A good alternative with a controller and lots of reasonably-priced indie games would be great.
The upcoming Dragonbox Pyra could be a great Linux portable machine running Steam (provided they provide ARM runtimes + ARM recompiled versions of games).
This is probably another issue. They definitely haven't started to deploy ARM version of games yet, even though there's numerous games that are 'ARM' compatible. Although, any game coded in Java and similar frameworks could in theory already run on top of arm versions of said frameworks I suppose.
