I think the most likely scenario is that there are many things besides resolution that differentiate the versions, but the marketing deal they have forbids them showing the ps4, or even speaking about the differences.
Even without a marketing deal, is there actually a common precedent of developers talking about system specific enhancements in any detail before a game comes out? Especially with regards to what are essentially graphical tweaks? I'm actually kind of curious. I feel like it's not something that's seen super often anyway, so that's maybe why the "show us all the PS4 specific graphical tweaks you're doing to show us your game is worthy" requests seem a bit odd to me.
I feel like with most multiplatform games, the unique system-specific details with regards to graphics tend to come out when the game is actually released, and in things like DF Face-Offs. Unless it's a non-graphical feature that's easy to communicate like Kinect support, touchpad support, or controller speaker support, I honestly can't think of any pre-release PR on a multiplatform game discussing graphical differences. Doesn't mean the graphical differences don't eventually end up existing, but it's just never seemed like a high priority part of the pre-release marketing push. One might even say...to avoid debates and stuff. Haha.
I could be wrong of course though. Oddly enough, I remember a game I worked on going through some controversy because of some "PS3 is awesome!" type comments pre-release, and then it turns out that the game looked a little better on the 360. So it does seem like there are some motivation to just not talk about differences too early on (especially since performance related items are not always locked down early on), and just let it all come out when the game is actually released.
I guess the weird thing about the Ubisoft dude is that he actually vocalized this idea, as opposed to just being quiet about it like every other game. It's not like WB and Monolith went into details about PS4-specific vegetation details on Shadow of Mordor during their pre-release marketing or whatever (well, maybe they did, I dunno. Would seem like an odd PR statement though, heh)
edit: NullPointer killing it right now, lol