Who cares what gen it "looks like" it's for? That is not even close to being the most important factor with one of these games as PS3 owners of F3, NV & Skyrim can attest..
As someone who has been on the Bethesda bandwagon since before Morrowind came out, no there is not really any excuse for Fallout 4 looking the way it does right now.
I'm not really a graphics nut, I mean I love Vanilla Skyrim as it is, the way it looks is fine and I've never had an issue with it even today.
But despite the fact I like what I saw in tone and setting for Fallout 4 and I'll probably enjoy the game just fine.
There is just really no good reason that a major title from Bethesda of all people should look like this in 2015. We live in a world now where a bunch of companies have mastered the open world genre to a point where you can make an extremely impressive looking game and also have it be totally open world, that's no longer a shock, and Bethesda with this reveal look like they're honestly stuck in 2012.
That's all there is to it, you can defend it all you want, you're right that graphics aren't everything and the game will probably play fine, that's not the point though.
But as it stands it just looks blatantly dated in a way that implies that they're either just fucking lazy or they've really fallen out of touch with then Open World RPG genre, I would like to think they'll come out and say that was an Alpha, because I can SEE where it can be easily improved on and polished, but such a lengthy trailer to me implies that this is probably nearly done.