That's not the entirety of the argument. Part of it, from what I've read, is that almost no one wants to risk a new IP at the end of a generation. I guess the idea is that you cut the legs off a release and thus make the potential of a sequel less than it would be otherwise.
As far as some IPs not really being doable on current gen, I can kind of understand, and the film industry is actually a good example of that. Early superhero films were horrible, awful things; it wasn't until technology advanced to a certain point that they could be pulled off in a way that didn't look absolutely stupid. There are probably certain concepts in gaming that are the same.