Problem is, sometimes people will respond to you without quoting you... because, for instance, they're posting right underneath your original post and (rightly) assume it's clear they're responding to you.
No search engine will ever link those two posts without a quote, I'm guessing.
Then again, I'm not into the nitty gritty of forum programming, so I dunno, maybe it's possible. And it would be a cool feature, then.