I've Spent Lots of Money on Halo

I've got some more substantive posts brewing, but in the meantime, here's a link to an interesting story over at GameDaily breaking down the money-making powerhouse that is the Halo franchise. Reading this, I realize that I've spent a crapload of money on Halo products. I have both Halo and Halo 2, all the map packs, the Official Halo 2 Guide, and a Halo Live headset. That's a lot considering that I'm only a casual player.

My big question is this: Can a game designer do anything to try to design this sort of fanatic product loyalty into the game itself (beyond just making a great product)? Is there anything about the game design of Halo 2 that lead to this or is it all due to good marketing for a solid product?