Even though Novels finally have their own category...it has yet to garner as much attention as web comics do in this site. Commenting works for both novels and comics, in my opinion. I see no reason why it shouldn't.
To encourage general commenting is no easy task. It has everything to do with the reader and their level of interest towards the comic or novel being read. So it's up to the creator or writer to grab their attention.
That said, even as creators and/ writers, we are still readers. I think if creators and writers alike supported each other by giving criticism/feedback, not only will they help improve each other but also gather the interest of readers.
It's like a street performer playing in the park. If one person joins, eventually, another will and when there's somewhat of a crowd...a crowd will soon form due to their curiosity.