Roland also got a feature (maybe Korg and even Yamaha too?) that counts DOWN during the Intro, so even if you forget, you know how many bars long the Intro is (they all vary!)...
Now all I need is link from the style to the lyrics and chord display, that would show the changes of the pre-programmed Intros, and all would be complete...
Probably the main reason you see the big demonstrators NOT playing during the intros is probably more due to the fact that they don't know what the intro is doing, rather than they don't need to play anything!
If there were a chord display, life would be a lot easier...