Kudos to Butcher, who pointed out these comments made by Bungie's PR Director Doug Zartman on halo.bungie.org's forum:

This seems like a good time to weigh in on this issue. The whole thing is a result of a miscommunication between ourselves and our friends at PC Action. A couple of our guys recently went on a European press tour, and during a visit, did grant permission for a videotaped interview, not anticipating that video footage of the game itself would be distributed. Apparently, distributing video footage of press meetings is fairly common in Europe, while it is not so common in the US - something we didn't understand.

Ahh, finally some clarification. The rest of the post explains Bungie's reasoning, and PC Actions response, which was very professional and prompt.