Same as any game, if WoW is fun for you... play it. If not, don't. Coming here and whining about how the developers of the most successful MMO ever "don't know" about their game (while amusing) is pointless. Clearly a lot of people disagree with you.
Back on topic, I like that I could go and create a 55th level character on the same server as another group of friends and hang out with them occasionally even though I still mostly play on my original guild's server. And I haven't seen any more DKs than I have Hunters or Druids once I got out of the lower level (55-70) zones. Obviously those are more highly populated with DKs than other classes because thats where the DKs start out.