Whoops, we missed this crucial part in the frenzy (can you blame us?). A second article, entitled 5 Things You Must Know About Microsoft's Buying Bungie, was also posted at the same time, and in my opinion, it is the far more important read of the two. An excerpt, right from the top:
2. Bungie may continue to publish games for the Macintosh and PCSeropian and Jones will make decisions as to what platforms each Bungie game will be released for. So far, no decision has been made for Halo or Bungie's unannounced third title (being developed in Chicago). In fact, it is not even confirmed that Halo will be an Xbox title -- though if it's not we'll eat our hats.
If you only read one of the two articles, read this one. And watch for more information over the next 24 hours, as Bungie and Microsoft (presumably) make their own statements on the matter. And most importantly, don't panic... yet.