Bringing up new hardware is a bit harder than that -- take a look at the most open example we have of doing so, the OLPC. 100% open hardware which they designed, but building the tools and bringing it up were still a lot of work.

Credit where it's due: the Android folks have worked very hard to make this an easy process for their OEMs.

By the way, this is why just about all hardware these days is brought up on Linux first. Yes, even your dear iDevices. :-)