I don't want my platform to restrict what software I can run, especially not based on license. Is there any mobile platform these days that doesn't try to be your nanny as well?
2) For many Android devices (kit from MOT excepted), the hacks are pretty trivial. I suspect the protections on HTC phones are more of a "Warranty void if removed" sticker than something to really bar you from gaining root.
AT&T (and perhaps other carriers) disable that option, but even in that case, there's a workaround that doesn't require rooting. (Google "android non-market adb".)
This is useful, and I think more of what the OP was looking for.
WebOS might be good in that regard, but its supported development model is limited to web apps so far as I know.