Halo might as well have bots too. It's got everything else you can pack in a title, ahead of its time with SP and co-op and skulls and online co-op and MP and forge and theater and firefight and external stat integration etc. etc. COD and Gears and a select few other titles are following suit, but they've been doing this quite awhile now.
Seriously Halo 3 was packed, and Reach went further. Halo 4 needs to add SOMEthing else. Why not bots? And a drink dispenser? And popcorn.