Really, whoever made that up must have smoked his brain away. Ok for little children and people that just go for a "walk" on a bike. But if you use it as a means of transport, then it's just dangerous to go on the sidewalk. What do you think would happen if I went 20-30 km/hour amid of pedestrians? Just crazy.
It should always be illegal to ride your bike on the sidewalks (except for little children on their play bikes that is), and only illegal to go on certain streets where it is actually too dangerous to ride a bike (like highways). But then there are no sidewalks along highways either, are there?