I think it has more to do with the game's target audience. More difficult MMOs tend to be unsuccessful while WoW is geared toward more casual players. Players hit 60 two weeks after launch and pulled 1-70 in something like 3 days after Burning Crusade.

The player that gets their jollies from Vanguard are going to get there fast. It's a good thing for the rest of us because they'll move on long before the bulk of the server gets to the end game. We'll have good siege experiences because we took our time enjoying the experience to get there, thus having an actual opponent.

Playing games with cheats is boring, same goes with a one sided RvR fight.

Besides, Destruction's popularity is irrelevant, the server is full on both sides. These super nerds happened to pick destruction.