A lot of those memes start off at 4chan or elsewhere before arriving on Reddit.
It is also gamed regularly, although I'm not sure how it compares to other popular sites. Upvotes are cheap to buy, and the type of feel-good stories that propagate are easy to mimic. Early up/down votes also have a hugely disproportionate effect, so cheating by getting friends/employees/social group to upvote your content is very effective - and has been abused blatantly enough by some companies to get banned altogether from the site.
It is also gamed regularly, although I'm not sure how it compares to other popular sites. Upvotes are cheap to buy, and the type of feel-good stories that propagate are easy to mimic. Early up/down votes also have a hugely disproportionate effect, so cheating by getting friends/employees/social group to upvote your content is very effective - and has been abused blatantly enough by some companies to get banned altogether from the site.