Ah, good point, I forgot about that. As a general rule, though, Card's novels aren't very quotable, and when they are, the quote is closely tied to the plot. If you didn't know how it related to Ender's development as a tactician and thinker, "The enemy's gate is down" wouldn't be a very impressive line. Meanwhile, Gibson throws off eye-popping lines every other page. Compare these two examples:

"Knocking him down won the first fight. I wanted to win all the next ones, too." - Ender's Game

If you don't know what Ender is referring to, this quote loses almost all of its power. If you've read the story, though, this line is killer.

"The Sprawl was a long strange way home over the Pacific now, and he was no console man, no cyberspace cowboy. Just another hustler, trying to make it through. But the dreams came on in the Japanese night like livewire voodoo, and he'd cry for it, cry in his sleep, and wake alone in the dark, curled in his capsule in some coffin hotel, his hands clawed into the bedslab, temperfoam bunched between his fingers, trying to reach the console that wasn't there." - Neuromancer

You don't need to have read the novel to appreciate the quote. Beyond the novelty and aesthetic beauty of the writing, it's very information-dense: You can get an excellent sense of the novel's setting, themes, conflict, and main character just from these three sentences.