I need to put in my 2 cents here. I'm not a "canon-ite". In fact, I hate the word canon. Religions have canons, not fiction. But I do think it is important to keep continuity as much as possible without hurting the story.
First; from what I've seen Abrams is sticking to the most important "canon" of Star Trek - the idea of hope for the future of mankind. I'm sick to death of all the dark future sci-fi. I have stated several times that I would have loved to see this new Enterprise look more like the TOS version but that's not as important as keeping to the spirit of the original show and it sounds like that is what Abrams is trying to do.
Second; I agree with some of the previous responses; The last few movies just weren't as good as the earlier onces and they faced stiff competition. Add to that, viewers were just getting bored with Star Trek. "Canon" was part of that problem. The writer's creativity was stifled by the amount of "canon" they had to adhere to.
Finally; I finally saw Nemesis recently. I had never seen it because I had heard it sucked, and it definately did suck. Not only did Nemesis repeatedly violate what I would consider Star Trek "canon" it was just plain AWEFUL science fiction. Case in point: After the Enterprise rammed his ship, the villian actually backed his ship off the Enterprise. Hello? As Heinlein would say, if you're going to write science fiction, learn something about science first!