They do have to check whether you are able to confidently, safely and within the bounds of traffic-rules, operate the vehicle close to the speed limits. This need not be taken to mean that one has to always ride close to the limit.

Of course, given that on two wheels, one is not as safe as on four (and also being enclosed in a metal frame). So, naturally the good riders will find ways to ride safely and that includes riding at appropriate speeds. The ones who aren't good/safe riders are not likely to ride for long.