Twitter is Slow, but not because of Ruby

Jeff Atwood commented on the Twitter scalability problem and blamed on Ruby's slowness. I have quoted from Coding Horror a few times (in my other blogs as well), but I still do not get how his opinions can be so highly regarded in programming community, when he cannot even distinguish between performance and scalability. Even he himself admitted that

To be fair, it sounds like most of Twitter's problems are database problems, so maybe it doesn't matter what language they use"

Even Alex stated it clearly in the Twitter interview that database has been the bottleneck, just like most share-nothing web development platform that was designed to be highly scalable in the first place! Ruby is slow. Python is a tad better, but in a heavily IO bounded web-based application, both will be more than fast enough. How to scale the database? It is not trivial and very domain specific, and that is what Alex is complaining about.