Does Android mandate this or can you go and create a phone that has none of the carrier restrictions you noted? I think you can.
1.) Restrictions imposed by Google, which you are free to ignore if you stick to just the released source code of Android (like the Market or their proprietary apps) 2.) Restrictions imposed by the Manufacturer (which you could ignore by making your own phone) 3.) Restrictions imposed by the Carrier (which you can presumably ignore if you make an unlocked GSM phone).
Working outside of all three of those restrictions would basically put you in the same category as OpenMoko (which while an enterprising idea was pretty much guaranteed to not go anywhere).
So I'd agree, "you" can go create a phone without any of the carrier restrictions, provided you are a handset manufacturer. I'm not a handset manufacturer, so I can't.
It's not cheap, but it's very easy. See, for example, http://www.htcphonestore.com/
Many of them don't have access to the Market, or run Google's applications, but I don't think that makes them "not officially Android".
Android source code is licensed under the GPL and Apache licenses and therefore the source code is open for developers.
The Android project isn't really developed in the open therefore the process is closed for most developers.
Most Android hardware is carrier locked, has proprietary firmware, or has proprietary services loaded on top and therefore is closed for users.