It's the Canadian motor vehicle safety standards that have to apply. You can't buy a European car if it doesn't meet the safety standards. So European carmakers sell thousands of buses here so they can modify their vehicle to comply with the CMVSS. But if we're purchasing a hundred buses, a lot of engineering has to go into them to meet the standards. That's why it's not done in cars.
On May 29th, 2012. See this statement in context.