1) With sub-reddits, this hasn't become as big of a problem unless a lot of users still keep the sub-reddits that annoy them. There is a reddit for everyone, especially since anyone can create their own sub-reddit. While Digg only had one idea tribe, Reddit has many. Moreover users that create their own sub-reddits can police them with other like-minded users.
2) Reddit is able to fit more content per page given their design. I don't have to keep clicking the next page link to get more.