(I hope it's more general, but this might only apply to situations of forced social interaction amidst a maturity level that isn't at its fullest potential (i.e., school) because only in this setting could you be familiar enough with a sizable number of people to know screen names and such but still be so distant as to hinder any conversation)
In the real world, there is a certain overhead to conversation. If anybody want talk to someone at a significant extent, they generally need to stop talking to anyone else, cease most other activities that require their attention, and place themselves within the physical proximity of the other party. Online, there is no need, and they can hold, for all practical purposes, an infinite amount of conversations without having to sacrifice on other forms of entertainment (books, music, games, whatever). Thus, people strike it up with others they would not usually find in their company. Thus, people talk to me.
In terms of raw social interaction, this would seem like a win-win situation, a great internet facilitated love fest, unswayed by such previous deterrents as time or status (after all, no one can really tell who you chat with). Sadly, that's just a little too idealistic to be true. Really, the physical constraints placed on a person's ability to socialize has an important (but arguably selfish) advantage: someone is most likely to only talk to people with whom they can most easily converse. When this is taken away, you end up with a facade, a pseudo conversation, people who have nothing to say to each other pretending otherwise.
So what? A semi-awkward silence (given the amount of external stimuli most participants have, lulls aren't as bad online), but then you move on. You've got your own circle of friends, and talking to them outweighs the failed interaction with someone you probably didn't even care about anyway, right? Yes, that's absolutely what happens, unless you're me and you're desperately trying to maintain the fragile illusion that you aren't a total loser.
I don't have that many good conversations in the rest of my life either, but I'm only passively reminded of the fact. Online, I don't have that luxury, and four line gems like these spell it out clearly enough:
: Hi
: what's up?
: Hey. not much. you?
: nah
Maybe there's more, but not much, and the talk just falls stagnant. Maybe I'm exaggerating here; I'm not hated, I'm not an outcast, and I can even make people smile a little or at least laugh. But still, this doesn't detract from my concern. Convenience devalues everything, and we just need more and more to sustain ourselves. How much is too much?