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
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.