OSNews

It's more than just that. For example, look at the most recent main page discussion: http://www.osnews.com/comments/26165

What does the first post even say, is there any real substance to it? I mean, it's "positive" of course, easy to agree with - but why is it at 9, the highest-rated post of the discussion? You don't have to vote.
Furthermore, note that a post fairly down the line ( http://www.osnews.com/thread?526160 ) is also quite high ...while, apparently, what it says and its source are not even factually correct - but it's something many would wish for, and overall it's still closer in nature to a one-liner that few earlier longish, interesting, and lower-rated posts.

No, it's also us, it seems that twitter-like messages are just more "effective" on people; probably we're just much less likely to read and/or appreciate the long ones - which required some thought to write them down, and require it when reading. Plus, considering how the short posts are less meaningful, less specific - they have that vote-whoring effect, more likely to be found agreeable by like-minded group.

Not artificially (? ...are there any natural moderation systems? ) restricting voting later in the discussion would probably still promote mostly-one-liners, possibly even more so.

Maybe, one day, a post-webcam technology can determine if you actually read posts before moderating, maybe coupled with separate "baskets" of votes (per post length category), and perhaps even neural monitoring to determine the effort both when writing and reading
I wonder how that would work out...