Archives are a start, but the problem is most channels are not indexed. There is no "google for irc" of sorts.
Even if the archives are searchable (the searches generally suck in the first place), who's going to know to go into this specific archive, for this specific channel, and search for this particular query?
As someone who was interested in this a few years ago: This is still an open problem for someone to solve. The solution isn't particularly hard, it's just nobody has really gotten to it yet.
(And yes, you may come across the odd irc conversation in your google searches once in a while - but it is not to scale with the immense amount of information that comes out of irc).
Oddly enough, I prefer the IRC channels I frequent to not be logged, just like the conversation I'm having at the corner coffee shop (probably) isn't logged beyond the ears of those who hear it.
To me it helps create more of a community feel. Often times you'll see active community members turn problems they deal with on IRC into blogs, articles or even books to spread that knowledge.