It's not so much the fact that they have DLC or that said DLC is expensive, it has to do with the way they shelled it out for the first game. First they say that unlocking Chaos as a playable faction would be a pre-order exclusive bonus. Which, already, is enough to piss off people looking at an $80 game and caused a bit of a split in the community.
Then the game launched, and the very week after launch they come out and say that you can buy the DLC to unlock Chaos, now suddenly shitting on the people who did shell out a lot of money sight-unseen so they could have the "exclusive" unlock. Didn't help that the original price for the DLC was something like $20 on top of the already hugely expensive title.
But then a little while later, people said "hey, for a Warhammer game, there doesn't seem to be any blood getting spilled", and they got the response that production had been a bit rushed, so it couldn't make 1.0.
And then blood graphics came out... As a $9.99 DLC. At this point people just said "alright, fuck you Mr. Scrooge" and boycotted the game because supporting that kind of behavior is fucking abhorrent. Then beastmen came out as another $20 add-on, but by that time the lines were already drawn.
So you see, it's not about the specific DLCs or however much they may cost, it's about telling the industry that those practices are unacceptable.
(This was all for TW:W1, mind. The second game just gets shit by virtue of association)