You forget to say that innovation is unnecessary. It's the quality of a game that decides if it's worth to play, not how innovative it is.
Partially true. Innovation can make up for lesser quality up to a point, just like good quality can make up for a lack of innovation. But for the greatest part, the game industry relies on polishing old designs and concepts until they gleam, and Blizzard has basically no peers in this category. Blizzard games (well, the PC ones, the SNES games were good for a different reason) have been "groundbreaking" because they are usually the best damn examples of X-type game that there is at the time. Not because they're doing hugely new things, but because they have incredibly high production values, consistent quality, and the most refined take on a given popular model - say, RTSes or MMOs.
Also, anyone who thinks that there isn't some innovation involved in refining extant game types needs to look more closely. Warcraft III had the best interface of the day, and is still one of the best. Unless I'm wrong, it was also the first RTS to have tab-selection withing hotkey groups, among other things. That's innovative, even if they're not doing something as relatively new as Sins.
Even the WarCraft cartoon style was filched from WarHammer.
Hardly. While much of Warcraft's (and Starcraft's, more notably) unit design was taken/influenced/whatever from Warhammer, the cartoonish style is anything but. The only way you could think Warhammer's art style or themes are cartoonish is if you actually LIVE in the grim darkness of the far future where there is only war.