Because the "foundation" can't be seperated from the apps that way. What is that foundation? What are the apps that need to be bleeding edge. What if I don't care what version of Firefox I have, but I must have the newest version of some tool or language. But now I get a buggy RC of Firefox and it crashes a lot. I consider Firefox to be foundation for me because I just don't care about it. But you may want Firefox 1.5 to be available TODAY. It is best to aim for bleeding edge or stability, because if you try to have both you will just have total instability.