@OP Bungie have and are making all except Halo Wars and the PEter Jackson one.
I guess considering what your post says you think the same about Half Life.
That has spanned 4 games for Half Life 1 and 4 for Half Life 2 (not including multiplayer games.
Halo has been around 8 years and only 3 games that to me is very impressive, not milking at all. By 2010 we will have 6 games. OOOOHHHHH milking it over a 10 year period. Ok.