I firmly believe that if they dont change the name to Halo 4: Reach they are losing 3+ million sales.
The problem with "milking franchises" is you isolate new fans form joining. Halo 1 2 or 3....its easy, somebody can go rent 1 or 2 catch up join in on the fun, it feel swhole its "main"...throw in halo wars, and ODST people see it dilluted, no Reach on top of that.
I think it closes people off from wanting in because it seems to encompassing in the universe, its not as inviting having all of these different games. I know they probably cant rename it since its a prequel, but i dont think this touches Halo 3 WW.