I don't know why people would get in a twist over this (or, even, the post's title, which is just stating the facts). I actually do find the situation interesting, as the (admittedly unscientific) poll on here before release suggested more people were going to buy it on the PS3. There are more 360s here in North America, so that probably accounts for most of it. And I'm not sure how aware in general gamers are of what is or is not the lead development console on any game. It's just as likely that a lot of gamers who don't follow the gaming press and post on boards like this simply don't know (or don't care to know) what the lead dev console is.
 
In any case, it's a good example of how multi-platforming a game can change it from a flop to a hit. All the more reason to expect that the golden age of the console exclusive is definitively over. That is, barring any significant change in the market. I imagine that more exclusives will become multi-platform (like, for instance, Mass Effect and GTA), and few new exclusives will emerge. Maybe that will change with the next console generation, but given the amount of money involved and the importance of the bottom line, devs will be highly resistant to influence from the console makers to produce solely for one console. We'll see over the next few years if this changes or not.

I'd be hesitant to say that it would have been a flop had it been a PS3 exclusive - I'm sure there's a fair number of people, several friends I have included, that opted for the 360 version because PSN was down even though they owned both consoles. I think that if it had been a PS3 exclusive you would've seen sales numbers that were a bit higher, but still nowhere near as high as multiplat. That being said, I love when third-party titles are multiplatform. I can understand first party exclusivity, but if a studio has an engine that can run across both platforms and the capability of porting it properly (in this case Rockstar handled porting the game from PS3 to 360) then there's no reason for them not to.  Poor Alan Wake. If only you had come out on PC and PS3 as well. Would have seriously helped the sales numbers.And not on the same date as RDR.