It's not glue, and many iPhone 4's were effected (notice I said 4's and not 4S's).
My first iPhone 4 had a really nice, bright display, I changed carriers and gave the old one to my mother. The new one I got had the yellow issue. It hasn't gone away, but it's not as bad as I first made it out to be. I took it to apple to get it replaced, and they said that there is a range of colours that the screen could potentially be, and that mine was within the "acceptable" range.
Like your phone, my phones yellow is uniform the whole way across. If it was glue, it would be more prominent in spots.
I'm hopefully getting an IP4S next week, so I'll see whether I have the same issue. Don't worry though, it will eventually stop bugging you and you won't notice it.