Then why do nearly none of them do it? Probably because they can't judge when they will stutter and lag - so many layers of web indirection.
The fact is, most web apps only a mother could love. The rest of us are sitting stunned and silent when someone shows off their latest "jewel" which stutters, lags, has buttons that don't react when pressed, takes 3-5 seconds to put up/take down a dialog based on a server database query...
