To be fair, you're very unlikely to ever have to solve the kinds of scaling problems Twitter has had to solve. You'll get your app off the ground faster with Python or Ruby.
You will get your app of the ground faster, but you're selling yourself short if you're a technology-based company thinking that you'll never have scaling problems. Competing against Twitter or any other social-based app you'll probably never encounter that level of scale, but any financial application will need to be both fast and handle the complexities that only the JVM can address.
Like he states at the end of the video, when describing the 7000+ tpm during the WWC:
"...we do things like Forex spikes upon our standard baseline growth. So right now the JVM is really the only mechanism that we can build upon that gives us the flexibility to do something like that."
Plenty of companies do huge transaction volumes on dynamic languages. Twitter is a freak outlier. If you try to solve problems long before you actually have them chances are you'll come up with the wrong solutions.
