The critical functionality in this application seems to be online calculation, i.e. he wants to know a player's exact rank immediately after insert. A sorted set is good for that.
In general I agree though. If you relax the consistency requirement slightly you can get away with regenerating the rank table every minute or so. It takes ~500ms on my machine to generate the ranked table for 500k rows on PG9. Unlogged tables in 9.1 would probably make it faster.
as sbov mentioned in another thread, the pro-RDBMS/SQL argument is that if i only reduce my expectation (admittedly slightly), SQL is a great choice doesn't seem too convincing. It's true that approach would be slightly less complicated (only 1 store, but now you have transformation jobs).
In general I agree though. If you relax the consistency requirement slightly you can get away with regenerating the rank table every minute or so. It takes ~500ms on my machine to generate the ranked table for 500k rows on PG9. Unlogged tables in 9.1 would probably make it faster.