For me, commenting is about engagement. I never even considered the idea of a comment earning income. However, I've found that my comments do, in fact earn income in an indirect way. Often when I comment on a piece, I notice the author of said piece will check out something of mine...bang, a read, and income. I've actually gotten most of my followers this way and even better, I've "met" some awesome people (while making a little bit of loot!) :)