You can still get electric scooters with larger engines. But I do believe that the cutoff for gas powered motors is 50cc.
The Gas/Electric thing is more based on how much each type sells. You find more gas ones with larger engines, rather than electric, but they still do make electric scooters that are classified as small motor bikes.
Plus, if you have a gas powered one that is capable of 60 km/h, you can go on highways (provided you have a slow moving vehicle warning on it), so you need all that stuff.
But like I said, I don't know all the details. My GF looked into it at one point, and her dad had a moped, as well.