I sincerely doubt that the top-poster has Twitter-level problems or resources. He may have a Rails site that's crapping out under load, and needs resources for optimizing both application performance and database access.
"Just move everything to Java" is a meaningless answer. It doesn't help him at all, not unless he's got a year and change to retrain/rehire his engineers and completely rebuild his application.
That's not really a fair comparison however. There's an non-negligible difference between just crunching messages, and then distributing said 6k messages/sec into a directed graph of users. Those 6k messages/sec is just the input, the output is far greater.