it's a feature, not a bug. The lousiness of it is it's main selling point.
For instance, sortings by low ratings and ordering from most recent is a trivial SQL query, but if they unleashed that then it would be much harder to hide the negative reviews. A good portion of that $300MM revenue is from the ability to hide the negative reviews. Hence, the lousy interface is a money making feature. You can build the competition with a better UI, but you won't get the revenue.
