You make an interesting observation about reviews not degrading over time. That would seem like something that benefit both Yelp and the places that are reviewed - Yelp's review averages would be fresher, and venues that may have greatly improved over time in response to low initial reviews would be rewarded with stronger-weighted recent reviews.
Yeah, I added a bit of a qualifier there to try to make it clear that I was talking about how humans read reviews - for all I know, Yelp reviews do algorithmically get less important over time. That'd be a smart thing to do.
