That's definitely not representative. Perhaps you've spoken only to guys doing HFT. A lot of trading systems are written in Java, and something like 20ms between seeing a trigger and sending an order to the market is fast enough for most needs.

I think for 24/24 operation though, the problem isn't really a programming one but simply the sheer number of people who'd have to work in shifts. Traders, engineers, middle office, maybe even compliance or quants... all these people are really expensive. You can't just leave a system running without people to monitor risk, check for reporting breaks, approve transactions, etc. The end of day reconciliations and reports are also much easier done with the exchange down.

You don't understand. Not everything is written in C. There's a backend system for reporting OATS that starts at 5 PM. If you need to make a non-trivial change you better not deploy it during market hours. Most of these systems are written in Java by guys who aren't at the firm anymore and didn't care when they were. You say cutting edge (which I would strenuously debate). But it's not magic -- in fact it's actually quite mundane when you get down to the nuts and bolts.