Not only does LuaJIT have platform-specific assembly in its source, but a big part of its advantage over PUC Lua is of course that it's compiling down to machine language on the fly. And that process is also platform specific. I have definitely seen bug fixes along the lines of "fix X for Y platform's JIT output."

I have also seen non-jit-related bugs impact us in production.

BUT, LuaJIT really is FASTER. Even when JIT cannot be used (e.g. on iOS), it can still be several times faster than PUC Lua.

And that speed is a real killer feature for us. Otherwise, we'd just use JavaScript.