While I agree that getting all militant about one company over the other is a bit silly, for those of us who don't really see much difference in the creative teams and are more interested in following characters, I would posit that focusing more on one company than the other allows one to not get punched in the wallet quite so bad when crossovers happen.
In other words, I've a theory that the more comics you were already buying involved in a crossover, the less one minds the fact that they did the crossover.