Spot on. That's a good way of looking at it - that the links act as topics. The comments are definitely the main value proposition (and addiction) for me.

This was true with Slashdot as well, now that I think about it. Back in the day it had the same draw for the same reasons. Though I think HN is a better version, since it doesn't have a few editors driving it like /. did, which was often frustrating.