Thank God I live in a state that doesn't require emissions testing. I think if they ever tried they'd have half the state up in arms. I think emissions testing is just another way for the state to inflate lisencing fees (and what's with those? Is a new car or truck really costing the state the $2000+ they typically charge over the first five or so years for lisencing a new car?). I can understand the reasoning behind emissions testing in urban areas when pollution is a concern, but should, for example, nourthern Californians, have to pay for SoCal's problem?
But anyway, to get off my high-horse. Yes, states can mandate stricter emissions, which California has been the leader in. All vehicles are required to comply with applicable emissions laws (my Fairlane is exempt, so I could :p if it ever came to it), some states just don't test.

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Once and future king:
'64 Ford Fairlane w/approx 238,000 - looks rough, but amazingly reliable if you know how to look after it; I will soon begin work to totally restore and modernize it.
Family vehicles that I lay some claim to:
'78 300D w/approx 350,000 original, '62 Ford F100 4x4, '90 Ford E150 w/171,000 original