The green light at the end of Daisy's dock symbolizes not only what's been said above, but also many other things. Jealousy, for instance. Gatsby was in love with Daisy, but he was also insanely jealous of Tom. It signifies greed -- Gatsby wanted Daisy all to himself, and he went to great lengths in an attempt to win her (Really, I'm surprised he didn't cut the books.) This is a slight stretch, but it's possible the light also symbolized, well, greenness. East Egg was full of those with new money (well, except for Nick), and while in that case it would make sense for the light to be on East Egg, then only those on West Egg would be able to see it and, well, it probably wouldn't mean much to them, being from old money and all.