Here’s an article from BBC. http://news.bbc.co.uk/2/hi/americas/6962970.stm In a nutshell – scooters take up less space than cars, both when moving and when parked. So they help decrease congestion.
The article is really about proposed congestion pricing in NYC, which is based on the London system. London’s system not only has exemptions* (so no fee) for motorcycles and scooters, but they also provide parking* for motorcycles and scooters. (Gee, what a concept!)
No one would doubt that moving a parked car is damage or attempted theft, but pushing over a parked scooter apparently is no big deal. One thing the article does not mention is that secure scooter parking is important because scooters are easier (than heavier motorcycles and waaay heavier cars) to hoist into a truck.
(*The source is Michael Horodniceanu and more answers can be found here: http://empirezone.blogs.nytimes.com/2007/06/08/taking-questions-a-traffic-expert-on-congestion-pricing/)