Well, this thread is a little premature. I mean we're going off of one week's worth of sales? Really? Shouldn't we wait til the end of the year, or at the very least a couple of months? Also, it's pretty obvious that Killzone hurt its sales on PS3 and the GeOW3 beta helped its sales on the 360. Now, imagine if Epic had a PS3 exclusive, which is the sequel in a very popular series (something on the scale of MGS5), releasing later this and put the beta for that game on the PS3 Bulletstorm. And then imagine if Halo 4 released last week and not Killzone. Yea, sales would have been reversed.
Another thing some may be forgetting is that Epic's whole ad campaign was basically mocking the COD series. Now COD is the biggest franchise this gen. Even bigger than Halo on 360 and GT on the PS3. Maybe the people who enjoy that series didn't really enjoy being indirectly called boring. In the end, I think Bulletstorm mainly appealed to a much smaller shooter crowd than Halo or COD, the ones who hate COD.