Well, that's not a meaningful distinction, because if I tell a javascript web app to turn something on and off every 1ms, the javascript web app will do everyth

Well, that's not a meaningful distinction, because if I tell a javascript web app to turn something on and off every 1ms, the javascript web app will do everything in it's power to do it also. It just doesn't have much power to do it. The real distinction is that a RT system is designed through and through to have a lot of power to do it.