Well, yes and no. Of course I haven't tried all 50 cc scooters, but most are restricted in some way to a
nominal 30 mph. The reason here in the US is that legally many states treat >50 cc scooters that travel at a speed less than 30 as a moped and the laws are more lax. Hence the reason that most 50 cc scooters are actually 49 cc's.
The state of North Carolina is one place where the law is really different since they do not treat a "moped" as a motor vehicle. No title, insurance or drivers license is required to operate one. Got a DWI? Lost your drivers license? Get a 50 cc scooter.
As for Europe, I do not know for a fact, but I suspicion that the reason is the same.