Those gaming websites are taking a big risk by voicing their negativity like that.
I thought negative previews/reviews on games with big publishers meant no more exclusives/early hands-ons/gifts and whatnot.
Or does that only apply to low scores?
It rarely happens at all. If you make a bad game, you expect to be told about it. If you punish critics for voicing an opinion that you don't agree with by blacklisting them, that generates a lot of bad publicity. Activision tried to do something similar to a French site, GameBlog, when they announced that Amazon France had leaked a posting for Black Ops 2 back in February. Acti demanded that GameBlog pull their story - GameBlog refused, since it's a gaming news site - and Acti blacklisted them and retracted their invitation to an upcoming press event. What does that say about Activision? Trying to censor news articles?
Gaming blogs report opinions as much as they report unbiased news. The comments sections allow other gamers to express their own opinions. So far, the opinions of TESO are pretty much "Oh look, another MMO that looks identical to everything else we've played in this genre." It's up to Zenimax to prove us all otherwise. E3 was their big chance for that, but it seems the gameplay that was shown only reinforced the standing opinions.