I don't think there's any laws regarding spare tires here- I think it's just intelligent. Both my cars have full sized spares which is good because I hate the little doughnut tires most cars have as a spare.

They are supposed to only be good for lower speeds and a short amount of time but I know people that leave them on for weeks before getting a real tire fixed or replaced.

Some modern cars like the Smart Car don't even have spares, but they do come with a sealant kit and compressor, which makes sense to me. Barring a catastrophic sidewall blowout you should be able to seal and re inflate just about any flat.

Of course if you get a catastrophic failure like that there's always roadside assistance that comes standard with most cars nowadays.
Def