Also, on raiding. It is harder, but not because the mosters hit for more damage or have bigger moves, but because of the size of it. A 5 man dungeon or boss could be just as hard as some raid content but getting 5 people who can play it right, learn the strategy, and not fuck up is ALOT easier then getting together 40 people who can play it right, learn the stratgey, and not fuck up. When you have 40 people, the chances of someone being the dick and causing the wipe is far greater. That is where the difficulty is, and you are rewarded with the uberist loot for being able to organize and pull that off.
The other thing is, is that the "UBER" loot really isnt that uber. Its purple and it might look really cool. The prestige of having it is what makes it uber. I tell you though, most of that raid and MC,Onyxia stuff isnt that great, and the set bonuses mostly suck. People see a purple con item with a cool name and go "OMFG" its uber, but really you could probably, or almost certainly peice together a set of armor with some random drops/crafted items, and enchantings and still be almost or just as good as the guy decked out in MC gear. Sure, he might look cooler, but that means nothing when it comes down to it. Blizzard did this purposly I think. They didnt leave out the casual gamer. If you never raid MC or Onyxia it wont really matter, your not gimped.