I'm currently using Django, and I can understand where they are coming from. The sheer amount of code that a simple request has to go through to receive an answer is staggering sometimes, such as 18 line tracebacks just to identify an authentication problem...
My own projects are not yet large enough to have this cause an issue, but I can see where something the size of Reddit would indeed have issues that even the most aggressive caching can't resolve.
It's not a matter of rating frameworks, it's a matter of purpose. Django and rails are designed to go from nothing to product as quickly as possible. Plus, thanks to better hardware and scaling techniques, it's easy and affordable to stick to frameworks longterm (instagram and github, for example). Sure, they could they rewrite their site in C++, Go or Erlang, but they would lose their ability to rapid prototype new features.
