I believe everyone on this thread that has suggested that people wait for another bus when the current one is SRO has also said that they themselves will wait for the next bus if they feel they need to sit.
We all make the choice to go to a crowded place like WDW knowing full well that there will be times when all of our needs are not catered to. I am an able bodied, healthy looking, athletic, 37 year old woman. However, if while waiting for a bus I have the misfortune of standing next to someone who has just finished a cigarrette, or worse yet is smoking one, I will have an asthma attack. Being prepared, I will pull out my rescue inhaler to stop it. For those of you who have never had to use such a thing, the medicine increases your heart rate. I am very tiny, and because of that this side effect affects me more than the average person, and my heart rate gets really high and I get dizzy. When you look at me you would have no idea what I am going through. I however need to sit down. If the bus gets there and I see that I am not going to be able to sit on it, I will sit on the bench (or the ground, if the bench is full - I don't expect anyone to give up the bench for me) and WAIT for the next bus. And when I get on the next bus, if I am still dizzy, I am going to sit down even if the rest of the passengers on the bus are 90 years old AND pregnant

I just hope that there are no DIS-ers on the bus, as they will just glare at me, and the stress may cause another attack. (For those of you who will take this last sentence seriously, this is sarcasm.)
Allowing people to even stand on a bus in the first place is not very responsible if you ask me, I am sure one of these days someone who was standing and gets hurt will sue, and the standing days will be over. If the lawyer is smart, they will also sue all the people who were sitting on the bus and didn't offer the standing person a seat, because after all these people shouldn't have been sitting in the first place....(again, sarcasm.)