I always folded my buggy if someone in a wheelchair got on. I can't imagine refusing to.
However, before I had kids I once saw a stand off between a whelchair user and someone with a very large buggy (honestly, it was like a tank) and from what I could gather, the pushchair was so big as it was a 'disability buggy' but the wheelchair user kept saying the mother should get off and eventually the mother explained whatever to the driver and he said to the wheelchair user that the child was disabled also. And the wheelchair user went a bit mental, stood up, folded their wheelchair up, stuffed it in the baggage bit, and went and sat on a normal chair
So yeah, its not always that straight forward.
Generally though, I do think people who refuse to fold prams for wheelchairs are twunts. Someone once had an EMPTY buggy in the pram space when I got on with Skye...she was a few months old and asleep and as he had no child in the pram I asked him to move...he argued the toss with me that it was 'inconvenient' to fold down the buggy then open it again at his stop...he was ON HIS WAY to pick a child up. What a ****ing dick. I told him this and he argued with me until the busdriver told him in no uncertain terms to move of get off the bus. What a douche...
We have James in a pushchair now if its going to be along walk as he tires out quite easily. I use the buggy spaces but if I see someone else waiting I will always put his down as he doesnt 'need' it as such. Even when they were younger I used to put mine down if someone wanted on who had a newborn or something as its a lot easier to shift a 6 month old than fanny about waking a newborn.