Yes they do. The motor will cut out at 15mph, but you can still pedal harder and go up to the speed limit, just without the motor, and since ebikes are heavier, I doubt many would be able to so they can only go up to 15mph.
Sure, you CAN illegally modify them, but most don't. So you can't "go any speed on an ebike"
Additionally, the speed limit is set by the law. And some really fit healthy cyclists can easily do 20mph+ without an ebike a d much easier. So really, any bike can go "any speed"
If a car has to exceed the speed limit to pass you, you're not going too fast, they are breaking the law. The car will need to wait behind you.