Tell that "law abiding" to VW.Haha this thread is crazy...
Bosch (maybe others) have it set in firmware so that if you have tire circumference, tire pressure etc all perfect the bike will go a tiny bit slower than legal limit but are still displaying 20mph etc.
They don't want you to be going faster than than the legal limit or else the law will come down on them. And with a zillion motors in the world, it's just too risky to bump it up a little higher, even if there is actually a tolerance permitted by EU law, etc.
So bike companies take on the risk by trying to introduce a bit of an offset to bring it as close to legal limit as possible. Maybe they don't get it perfect of course, or they don't even bother to mess with the motor supplier defaults. But the dealer is able to adjust the circumference by +/5% and get you the 1-2mph that is missing. It's really that simple. German companies are very law-abiding