I'd say that was also because those games were running at below-native HD resolutions. Thus, I don't think you can compare it so easily.
720p in of itself doesnt generally mean much IMO.
If we're talking about direct comparisons between PS3 and 360, i'd say the pixel differences were very much a factor, but of course AA solutions matter two.
Take BLOPS1 for example. Neither 360 or PS3 were HD, but because 360 reached the same res as previous 360 CODs did while PS3 had to be reduced to Vita's native res(like 954x500 something), it really mattered.