Halo is as synonymous with Xbox as anything could be, and maybe more than Microsoft ever thought it would be. Game consoles don't really have mascots anymore -- apart from Mario, arguably -- but if the Xbox had one, it would be Master Chief (sorry, Kameo). Microsoft is perfectly aware of the explosive popularity of Halo, which is evident if one simply looks at all the Halo products currently available or on the way.
For the moment, let's forget about the books, the toys, the board games and the comics. All of them (with the possible exception of the upcoming Mega Bloks) are aimed squarely at the demographic that loves the game. I only exclude the Mega Bloks because they are aimed (I assume) at a younger crowd than Halo's M rating should cater to. While one could argue that Microsoft and Bungie have spread the brand too thin, that Master Chief has sold out, the games have always remained solid. After all, we still haven't seen Halo Kart or any Halo sports games (Grifball notwithstanding). At least not yet.
So, with the advent of Halo Wars, Microsoft has used its secret weapon to push real time strategy into the arms of an audience that might normally ignore it altogether. That's not to say that there aren't well-rounded Halo fans out there that enjoy all types of games. I just get the feeling that the people teabagging me probably didn't grow up playing Command & Conquer or StarCraft. That said, is Microsoft sacrificing the Chief's soul for the sake of making a few more bucks off of him? Does Halo Wars dilute the brand?
Fundamentally, no, it doesn't. As long as the level of quality we've come to expect is preserved (pistol nerfing quibbles aside), Microsoft should use Halo to expand as many genres as possible (as far as I'm concerned). Of course, it remains to be seen if Halo has the power to make console players flock to the RTS genre. Considering the first Halo helped usher in a new era of console-friendly FPS games, it's certainly possible. Assuming Halo Wars has what it takes, I say Microsoft should start planning its next genre buster right now. Maybe a golf game or something.