ME3 has some huge environments, increased texture detail and more complex shaders on the characters, all of which is evident in screenshots. Lightmass prebaked GI seems to be missing but then again the softer look and color bleeding wouldn't really fit ME's unique mix of retro and current SF visuals. I'd also rather have the game next March instead of, say, next September
Bioshock has a heavily modified engine, I'm not sure how much of UE3 is left in there. To be honest I think we're still not seeing much of the tech advancements in the current games, Epic had at least an entire year's worth of advantage in content creation because they were able to start asset production before the upgrades were completed. Other studios only had a chance to play with them well after Gears 3 was in full scale production.
And what other big franchises are on UE3 anyway? The best selling multiplat games are COD, GTA, Assassin's Creed, Final Fantasy, Fifa, Battlefield, Elder Scrolls, and they all use custom tech.
So apart from the (exclusive) Gears games, Epic doesn't really have any big sellers running on their engine in the end, excluding Mass Effect and Bioshock. Okay I'll give you Batman too, assuming that Arkham City becomes another hit.
So I think that's why we actuall don't see many games using Lightmass. As for other engines, a lot of them opted for fully dynamic lighting (COD, GTA, BF, Elder Scrolls) or they wouldn't profit from that because of their style or setting (FF, sports games, most of the other platform exclusives). Actually almost any game using deferred rendering and a lot of lights has probably decided to do so because they don't want soft lighting and lots of color bleed which Lightmass seems to produce.
And I believe it's more about the GI settings anyway, number of extra light bounces, amount of color bleed and shader settings, and so on... It's more of an artistic choice, which took a brave leap from Cliff's team on Gears with its harsher looks in previous games (hence some people believing that Gears 1 looked better, muhaha).