Why else would you do a reboot if you are not going to recast the character's. There was no real need to recast the Incredible Hulk but they did, and the characters fit more than these do.
All that said, I have no problem with Routh staying and everyone else leaving. It seems like he is getting plenty of work now so he doesn't need the role anymore.
What we need now is a predictions thread, so we can start predictions on what will happen, so we have proof of who was right and who was wrong.