That's pretty much the same anywhere that chose to regulate it. It's about delineating between licensed and unlicensed users, and keeping a segment of vehicles off the footpaths. They essentially had to put the line in the sand somewhere, and they chose 25km/h. I can easily pedal faster than 25km/h, but the speed isn't really the whole point just a means to an end for regulatory purposes.

That line in the sand does a few things:

* Makes children ineligible for powered riding over 25km/h

* Forces anything powered faster through the right safety standards testing

* Applies a whole new segment of laws and penalties to your riding

* (in my country) forces you to wear a helmet that could actually stand up to an accident on the road

* Makes you join the liability/insurance infrastructure of licensed road use

In a car first community (like most of the US) I think it makes a lot of sense, in a bike focused community I think it's worth debating a bit. It would be great to ride a long separated bike path at 30-40kmph powered to work. Dreamy. But that's pretty rapid at the scale of humans and bikes, 40kmph anywhere but a separated bike path is just asking for trouble.