The current scenario is that many cars either have what is called a 'spacesaver' or no spare at all. My own Volvo has a spacesaver which is basically a steel wheel with a narrower tyre. The main reason is that the car itself has wide low profile tyres fitted and these are bluntly huge.Even with alloys they are pretty heavy to handle, so I suspect that the installation of the spacesaver was a compromise by Volvo. If I fit it I can drive at speeds up to 50 mph, although it is recommended I get the original wheel and tyre re-installed as soon as possible. As it is a brand new wheel and tyre I suspect it would get me quite a distance if required.
The other scenario is no spare at all and you get a can of aerosol foam which is supposed to re-inflate the car tyre, and get you home. This is common on cars such as the Smartcar where the front and rear wheels are of different sizes, so a normal spare is not practical. It is also common on many motorhomes as the spare wheel is huge and space may be limited. It is also not always possible to change the wheels at the roadside, so if you are calling out the breakdown service anyway, they can sort the whole problem out for you.
The other thing to bear in mind is that many alloy wheels require tightening torques of 100 lb/ft or more, not your normal quick twist.