ShamelessC parent
Yeah this is confusing to me because they imply you need a certain score to get on the front page but I'm seeing plenty of links on my front page with very few upvotes.
The decay rate for front page items has always felt off to me. Quite often you'll see articles with 20-30 points and no comments camp in the middle of the front page all day, while more actively discussed items drop off.
Comments don't affect story rank, with the exception of the flamewar detector mentioned in the sibling comment by krapp. It's not uncommon for certain kinds of story to get plenty of upvotes but no comments. Those stay on the front page for a while. I think that's fine; something can be interesting even though we don't have anything to say about it.
Items with active discussions are often implicitly penalized, because the number of comments are often greater than the number of upvotes, which is interpreted as a sign of low quality discussion or possible flamewar.