[dsil]

I can think of 2 reasons for this. One, like you said, people don't seem as quick to post the "first thing that comes to my mind" sort of comment, which tend to be fairly shallow, or pun or meme-based.

Also, it doesn't take much for a story to get to the top, if only briefly. 5-10 up votes on a story shortly after it was submitted can get it near the top of the front page. It takes many more votes to get to the front page of a site like reddit, so more likely one of those up-voters commented as well.

[psyklic]

This is likely because you must open two separate windows -- one for the article, and a second for the comments. often when i read an article in a separate window, i want to make a quick comment but decide it's not worth the effort to find the comments page again!

of course, this is remedied by some FF plug-ins, but i doubt most users have those installed.

[diN0bot]

when i first moved here from reddit i ran into this problem a lot. then i got slightly annoyed at having to have twice as many browser tabs open as before. i still don't use the plugin, but it has ceased to be a problem. my friends and i joke about having to get through all our tabs before getting down to the brass tacks.