I don't mind DLC really. Sometimes if a game is good, and you want to get more content, you can buy more. If the game is craptacular, don't buy the extra content. Borderlands does this really well i think.
With regards to the AC DLC, as long as the version without it still functions as a game, then that should be fine. If Sony and Ubisoft want to agree a fee to give extra content on their version of a game to get more people to buy it on that platform, i say go for it. No-one complains that it's unfair that Halo isn't available on PS3 or that Uncharted isn't available on Xbox360. They are exclusives. That's how it works.