People won't comment if they feel they don't have anything of substance to add - sometimes submissions can stand on their own pretty well and thus don't solicit a lot of comments. It's about maintaining a high signal-to-noise ratio. If anything I've found that you can use the karma/comment ratio as a moderately reliable indicator of link quality.
As for your original question, you should probably "lurk moar" before starting off-topic discussions. This really isn't that uncommon.
1.) See headline 2.) If the user enjoyed the read, they click upvote 3.) (Maybe) comment
What you are suggesting is that it's more like this:
1.) See headline 2.) Click upvote 3.) Read link 4.) (Maybe) comment