I assume that there is some kind of regular road worthyness test for vehicles in the US, in the UK all motor vehicles over 3 years old have to have an annual test.
Cars are tested for emissions, where motorcycles are not, as standards are changed they are not applied retrospectivly, so a 1960's Mini is expected to not belch out clouds of smoke, but wouldn't be required to achieve the CO2 emmisions of a 2009 Mini, the same applys to braking standards etc.
Most people are happy enough with the system although it can be a bit of a chore (Vibrac will have an opinion) but there is no restriction on the use of old vehicles or modifications, as long as you stay within the general rules, so you can fit disc brakes to your Bantam but fitting Bantam brakes to you R1 would be a no no.
Recently the UK govt decided to remove the need for the annual test (MOT) from all vehicles manufactured before 1966 and there has been some debate about this on the forum, some of us felt that it took us out of the mainstream and could lead to restrictions on where and when you could use the vehicle, the govt is now saying that you can still have a test but it wont be mandatory.
Most of the stuff in the Euro proposal is no different to the standards currently applied in the UK, however the proposal to class old vehicles, 30 years is only 1982, as a special case is the worry, especially if they cant be modified from standard.
I believe that in some Euro countries there are already restrictions on the use of older vehicles,but I'm not sure where or what the age threshhold is.