I think myself that for once the eastern states have it right. Power to weight restrictions are the way to go rather than a certain size.
Take motorbikes for example. In the east a learner can get on certain 400s without a trouble but then something like an RGV 250 they cant ride, but here they can.

How many RGV's are there left now that are in decent nick? Fuck all. First time I rode one it scared shit out of me as I thought, meh its only a 250. (Note, it was modded as well.)

I have heard the arguement that farmers need their sons to have a license to drive the V8 ute to pull trailers etc. Well you can get more than enough torque from a deisel.