what sets them apart, besides the numbers?
Use the site, find out. It's like asking what the difference between Moby Dick and For Whom The Bell Tolls is. They're both books but they're vastly different. Can't point to just one page to say how or why, you need to read them.
While there are tons of differences between the two sites, I'd say there is one big thing that separates the two: No downvote button. The downvote button, while useful in certain circumstances (such as dealing with trolls), pushes actual content to the bottom and even hides it if no one agrees with the statement. Here, the only way to show disapproval of a comment is to voice your opinion, which stimulates conversation. :)
interesting point, definitely agree :) Also, Hubski users have the option to ignore users and specific sources of content that they don't want to see. On reddit, a mod or admin has to manage that.