but now they're 3 generations behind?
Not really the same idea. This is going by the thinking of the average consumer, who Microsoft is trying to market towards alongside gamers.
If they see Xbox One being sold alongside the Playstation 4, they probably won't be thinking the Xbox is a really old piece of hardware, because hardware cycles aren't terribly long. The thinking would probably be closer to, "This must be a new product line."
If they see Xbox 3 and Playstation 4 being sold alongside each other, they may think the Xbox is a year or a hardware cycle behind the Playstation, cause that's not really out of the question.
That's how I see it anyway. I seem to be part of the very small minority that doesn't totally hate the name.