I know im replying a bit late, but...
How did Treyarch fix glitches? Name one glitch that they fixed (From cod4)
Just because it has different maps doesn't mean its not a re-skin, if they took the same maps from cod & cod2 the multiplayer would be a whole new level of bogus. And im talking about multiplayer, not any of the other game modes, i love me some zombies. All im saying is that cod4's multiplayer is better, and w@w wouldn't have perks create-a-class, challenges and many more things without cod4.
Because it's a franchise. Call of Duty is a franchise. Without 1 there would be no 2. So yes, World at War took to new ideas from CoD4 and then added their own features as well. Just like MW2 took some ideas from World at War and added other new features. That's why Black Ops has camos, some similar ideas for killstreaks, and callsigns. Just because it's a different company making it doesn't mean it all has to be different. Ya know? :)