Gas-guzzling luxury cars and big SUVs could be withheld from the Canadian market in coming years if Ottawa makes good on threats to impose fuel-efficiency standards, auto industry representatives claim...If the popular models weren't available, people would keep their cars longer, he [Dennis DesRosiers, an independent auto industry analyst] predicted. That would harm the environment because older cars are less fuel-efficient than new ones...Environmentalists say the voluntary approach hasn't worked and legislated standards are overdue. [refers to General Motors]