One, this is a major feature to add. Keywords for every language under the sun, with context-sensitivity (to know when you're asking about a given feature)? Entire class libraries? This could get freakin' huge -- and for not a lot of payoff, in my mind.
That, and generally, "RTFM"-type (or the more modern equivalent, "LMGTFY") answers are frowned upon to begin with. It's often been said that Google is StackOverflow's home page -- that is to say, so much of their traffic comes from Google searches that kicking someone out of the StackOverflow environment (even if not to Google itself) is probably not the right approach.
Often, there is a deeper question. Sure, API
x might cover everything they need, and pointing them at raw docs might be OK. But a lot of the time, I've seen that people are more interested in how to apply API
x to suit their needs, and that's information that may not be readily apparent in the man page.
Finally, again, the SO goal is to be THE repository for this information. Yes, much of it may be repetition of "what's out there" -- but the goal is to make it so that SO is the one place you as a developer have to go. That, I think, is part of why the FAQ specifically says that no question is "too newbie."