Tornado relies on a small number of well defined system calls (such as epoll). For me, the difference between reading (and debugging) a few hundred lines of cod

Tornado relies on a small number of well defined system calls (such as epoll). For me, the difference between reading (and debugging) a few hundred lines of code down to the system call level, and reading (and debugging) a big library like Twisted is rather significant. For you, the difference may not be important, and that's fine. I also don't think that it's necessary for Tornado to replicate all the functionality of Twisted -- if people want Twisted, they should simply use Twisted and ignore Tornado (and hopefully the Twisted team will have borrowed the best bits of Tornado anyway).