You need to look at the average reply rate instead of the request rate. Requests/sec can be misleading. The replies / sec tell quite a different story. Here they are for pong:
Rails Webrick: 153.9 Rails Thin: 33.3 Rails Mongrel: 90.7 Rails JRuby (glassfish): 3,350 JRuby Mongrel: 31.3 Snap: 11,309 Play: 19,796