Depends on the bus company and ticket type, batman.
Round here a day rider is cheaper than a return from my home to town, and bus every ten mins, so yes, getting off and waiting for the next bus is fine, also is in town, so good pavements, well lit, and I could walk on to the next stop no bother, too.
Some places I've lived in, the busses are spaced much further apart, as are the stops, over areas with no pavements or street lighting, and day rider type tickets more expensive an the journey you want to make itself. Then the bus company takes your money for a service it then can't provide (think rush hour, rest of bus full, so actually you're taking up less space from other passengers by staying in the bay until the wheelchair issue arises - see this on the busses here much more often than a wheelchair user using the space by the way). If the company would also expect you to pay again to try and complete your journey (because of course the same could happen on the next bus, especially at peak times) would that maybe change some peoples perception of "fair".
Should there be an imperative on the bus companies that if a passenger has to get off for another passenger that they should then get the rest of their journey validated? Of course, but it doesn't always happen.
If you've already been told to get off three busses you've paid for that day/week, should you nod smile and say of course when asked to do it again, to stand in the dark and rain on a verge with no pavement with a child in a buggy and maybe another one to wait half an hour to pay again for the privilege of having another go? Would the bus company not be held liable if anything happened to that family while waiting for the next bus in a less than safe environment? Should they be? What if the bus in question is the last bus to a particular village the buggy user is trying to get to, but the wheelchair user could take three other services from the same stop within 10 mins for his/her shorter journey? Outlying areas last bus services are often a lot earlier than city dwellers realise.
I suppose I'm saying there needs to be a carrot proffered by the bus company as much as a stick of "enforcement" from the courts, and that there are more factors to be considered than the daily fail generally reports.