Chances are the person who did that demo didn't play it directly on the Tyros 3 from the keyboard. Most often these demos are put together using professional studio musicians with MIDI guitar interfaces and other MIDI converters so that live musicians are playing live parts that are then recorded using the sounds from the instrument. It's a very deceptive and common practice because even if you were a truly gifted incredible player (which most people aren't), mimicking the part directly from the keyboard would be impossible.

From the demos the Tyros 3 sounds good so far but I'm not hearing it do anything that my Wersi doesn't do much better. Until Yamaha makes an arranger with 1GB+ of factory ROM for the sounds I don't think Wersi has anything to worry about.