I would expand that to say that lua has a standard library and framework problem. You can link any old C library but there's little uniformity in how everything fits together and rather few task-oriented packages/frameworks exist.

I like lua and am using it for some tasks where I'd have used C in the past. But for many things where ruby/python have strong, pluggable libraries (e.g. everything web-related) there is simply no equivalent in lua-land.

Kepler project is nowhere near a django or rails.