I think the people that have had their stance change on BO vs MW2 are probably just sheep riding bandwagons. It was all the rage to hate on MW2 when it was out, screaming how noob the game was, and now its all the rage to complain about how much better it is, and there seems to be not a problem with it.
MW2 has always been bad. But as I have been saying since it came out (I found my old website with a review I wrote the day the game came out, and to this day every word holds dead on) the game is fun, but flawed in many way. Lag being the main one, and lack of dedis being the second. With alter fixing both those problems, its now just a matter of how players play. For the most part, I dont see a lot of abuse of the broken mechanics in the game. Especially now that everyone is done complaining about them, its not any fun to piss people off anymore.
So the only way MW2 has changed, is that the players have stopped abusing some of the broken gameplay elements as much. MW2 is the same game, plays just as smooth as it always has, and the only reason people hate BO now, and think MW2 is flawless, is because the bandwagon for hating on the newest CoD game is rolling around.