Halo set Microsoft up in this business. It sold a ton of Xbox games, and more importantly, it sold a ton of Xbox consoles. Halo 2 did the same thing, Halo 3 did the same thing again, except this time for the 360. Everybody knows that. And if everybody knows that, you can bet Bungie know it, and community lead Brian Jarrard isn't shy about asking "Could you imagine the Xbox or Xbox 360 without Bungie’s Halo?":
Bungie knew that Halo was a fun game, a game we really liked, but had no idea it would turn into what it has become today, let alone single-handedly make or break Microsoft’s entry into the game console market.