The analogy to full scale aircraft, trains, highways etc seems essentially invalid anyway, given that we are talking about speed limits that are not applied to all R/C model aircraft, but only those that are turbine powered. For the anlalogy to hold up, the equivalent full scale rules would have to be something equally weird, like:

[ul][*] Trains that are diesel powered may not exceed X mph, whereas trains powered by electricity, etc may go as fast as you want.[*] Cars that run on high octane fuel are limited to 65 mph on the freeways; cars powered by low octane fuel, natural gas, etc., may go as fast as you want. [*] etc
[/ul]

Gordon