Less than 1% of readers leave comments unless they feel they have something to say. Controversial issues like terrorism, wikileaks, racial issues, immigration, and so on gets more comments. Some scam-related hubs that criticize a particular scam often will attract "supporters" of that scam to defend the scam.
On the other hand, some comments are just covert ads... They post something like "nice blog!" and add their own URL advertising something.
I've known some hubbers who drive up their own comment count by responding to every comment, often with something as inane as "thank you for commenting!"
So don't worry about it. # of comments are NOT related to how good your hubs are.