Correct me if I am wrong but the PS3 was more powerful than the Xbox 360 but harder to code for, so in a way the only reason a game would have been better on 360 would be because of developers not dedicating the time to a game. Just look at what PS3 exclusives achieved.
But yeah I agree it's lame, 1080p should be the minimum these days.
Too late for excuses, the cat's out of the bag. And as your link says, they managed 1080 on the PS4 with a patch after release of Watchdogs so it is possible.
The thing is, Watchdogs received similar criticism and also had a ton of NPC's on screen but were they all necessary? I think it's great when you first turn Watchdogs on and see streets packed with people, but after playing for an hour it became quickly boring with 70% of them offering nothing but lame social commentary. On the other hand, Infamous: Second Son looked great but probably could have done with a few more NPC's.
I think it's the type of games that both Watchdogs/AC are that is the real problem. If the new consoles struggle with their vision then so will half the PC market, so you have to ask yourself why they comment like this at all? Let the game do the talking and the buyer decide.