> Samsung, whomever can and do modify the code -- those modifications aren't generally open source.

That will certainly change quite soon. In the earlier days, FOSS was not a concept that masses were aware of, but now is different. There is increasing competition in the smart-phone world and if one of the other manufacturers (say ASUS) makes their Android modifications open-source, they will see a drastic increase in Sales. To keep up with competition, Samsung, etc. will also have to do the same. In other words, competition will ensure the success of open source.