Pithy and sounds good, but totally discounts network effects. Programming languages are subject to network effects -- users create libraries in the language, increasing the usefulness of the language. Of course, interoperation between languages is possible to some degree, but that doesn't detract from the core statement.
It's really not hard to use C libraries from Lua, and its design for embedding / use as an off-the-shelf extension language has made interfacing easily with other languages a high priority.
There are projects that supposedly allow interoperability with Python, Perl, and several other languages (http://lua-users.org/wiki/BindingCodeToLua), though I have only used the C API thus far.
The core language is also small and simple enough that adding major language extensions, such as Erlang's concurrency model (http://concurrentlua.luaforge.net/), is feasible.
