Well PostgreSQL does scale to millions of simple read-only transactions per minute, at least in some benchmarks. And in PostgreSQL 9.2 it will scale much better, in the synthetic benchmark it reached about 13 million per minute at high concurrency (compared to about 2.5 million for 9.1).
It's been amazing watching the performance surge in postgres these past few years. I wonder if Red Hat or similar will try sponsoring a tilt at the TPC-C crown in future.
Back before Sun bought MySQL they started doing a lot of performance work on Postgres. They didn't go after TPC, but they did show it was only(?) 12% slower than Oracle for SpecjAppServer: http://www.informationweek.com/news/201001901
http://rhaas.blogspot.com/2011/09/scalability-in-graphical-f...