You're a bit off here. Appcelerator doesn't actually compile ANY javascript to native code. They expose a device specific API via a proxy/bridge system they call Kroll. They have a bunch of ObjC code that they then front with their Kroll Proxy. They also have a small shim between their JS interpreter, and Kroll on the other side.
So in effect any app you run on Appcelerator is still bound to the characteristics of their chosen JS interpreter, AND the characteristics of their proxy, AND lastly the performance of their native API.
It does provide a relatively simple path, to getting relatively simple apps up and running with native widgets but not inherently native performance.
Disclaimer: I've only ever dug into the iOS source, I can't swear this is 100% valid on other platforms.
So in effect any app you run on Appcelerator is still bound to the characteristics of their chosen JS interpreter, AND the characteristics of their proxy, AND lastly the performance of their native API.
It does provide a relatively simple path, to getting relatively simple apps up and running with native widgets but not inherently native performance.
Disclaimer: I've only ever dug into the iOS source, I can't swear this is 100% valid on other platforms.