This was discussed here. There are more proprietary components making up the base of Maemo than there are Android. They both have proprietary drivers, but some of the other parts of maemo that actually make it function are closed off as well. The base Android OS is totally available for anyone to compile and use and put their own drivers in place. Plus, using things like xda-dev's isn't the best way to express "openness" considering, as I mentioned elsewhere, cyanogen got a Cease and Desist order from Google for distributing their proprietary software (maps, market, etc).