Not to mention this game is practically a part of pop-culture at this point (CMN.. it's been on
And to add to the fuzziness... Halo 3 is also a console-selling game... they are spending 10 million in marketing to sell a game that will also sell a console. Assuming the marketing is done even remotely right (and seriously... the game sells itself... MSFT bashing aside... they could screw it up and it still won't hurt sales too much at this point), then they are likely to have an increase in console sales. People who were on the line about getting a second console (basically people who bought a wii) or getting their first console might be convinced that this is the time to get a 360. Either way, Halo3 is a big enough title that it's going to sell both a large volume in the game itself, but it will also boost sales for the Xbox 360 console for an extended period of time (including Christmas time at which point all stores will be fully stocked with both the console and the game)... and... well... that makes the prediction/fuzziness/math even harder to pinpoint.
Considering how strong the competition is and the fact that they will undoubtedly make a strong profit margin on this game, spending 10 million to promote it seems perfectly fine considering more money on advertising will eat away at people's willpower (to buy both the game and the console) much more than a $10 price cut would.