You can recompile software for a different architecture relatively easily. You can't easily rewrite GNU/Linux software to run on Android.
EDIT: I think you still don't understand. It doesn't matter what hardware Android runs on it's written to be appliance firmware. Even if you put it on a laptop it just turns the laptop into what is essentially a television.
But now that you say it, Android is very much a full OS. It's not a Linux Desktop, but it is a full OS. And televisions running Android are called "smart TVs", precisely because they run a full OS instead of a minimal firmware like they used to.
Google is working on bringing Android to the Desktop, and Samsung already does it. As in: you plug your smartphone into a docking station and it is suddenly a Desktop computer.