They're slightly different, yeah, but actually I don't see kudos as variant in meaning. I usually take it to mean "I liked this, thanks for writing," which, honestly, is pretty much the content of most of the comments that I leave and receive. And, if you take kudos + comments as a unit, the institution of kudos has resulted in an uptick of fb on my things at AO3, which is pretty awesome. So, I honestly don't think of them as "less than" a comment or resent getting them instead of a comment, and most of the people I've read around seem to feel the same way.