My assumption is that people who say shit like this haven't spent a lot of time listening to The Beatles (which is fine, whatever), mostly because their palette isn't adjusted to older music with lower production quality, etc. And because, in 2012, listening to their early stuff does feel really dated and kind of vapid. I mean, to really appreciate their work, you have to listen to like A Hard Day's Night and go on from there. And at that point, they become less accessible, and I can honestly see why someone who listens primarily to pop-punk or like modern pop music (which is fine, whatever) would have trouble getting comfortable with a lot of their later work, since it is, by and large, pretty complex in its structure and arrangements (especially when compared to like Saves the Day or whatever). It just requires more of the listener than they're used to, and so instead of putting in that effort (or maybe they just don't know how - which isn't an insult or criticism, btw), they just immediately dislike it.
In the end, it obviously doesn't matter what other people do or don't listen to, but I just don't understand why they feel the need to make claims like the band is "overrated" or, worse, not any good, when that's just objectively wrong. And I'm not even like a huge fan (I only own like two full-lengths and a couple of "hits" collections), but c'mon.