If this is considered OT, then I apologise and mods feel free to remove.
As some have said, "assistance" covers a broad spectrum - and I can talk to my own experiences as a blind (oh sorry, visually impaired) person.
To be clear - I see nothing, nada, zilch - not even whether the lights are on or not.
My eyes, however, are the only body part that doesn't work well.
I travel frequently, and one of my personal gripes is being forced to wait for everyone else on the plane to get off before the "asistance" is available to guide me through the airport.
Even then, insistence on putting me in a wheelchair or buggy when I am fitter than the average person is: a) infuriating as I actually want to stretch my legs and b) somewhat embarrassing.
I am fortunate enough to travel, more often than not, in business class or first cabins and it drives me mad to have the facility to get off amongst the first passengers to leave but being told to wait until the entire plane is empty.
I need to shout out to BA here - one of my carriers of choice - when I explain this situation to cabin crew, often-times a member of the crew will actually escort me through the airport immediately after landing and I am able to get off the plane just like any other passenger (I have sent complementary messages to BA naming the staff that went above and beyond but have never received acknowledgement so can only hope the staff concerned do learn of my complements).
US airports - well there's a whole new topic - very helpful yes, but they have one way of doing things and you'd better comply with that or be prepared for a hard time!
I am not unreasonable, "assistance" is an additional service that the majority of passengers won't need and you could therefore consider it to be reasonable that one would need to wait occassionally, but my experience is, apart from helpful BA staff, that you always need to wait (up to an hour sometimes after doors open).
A couple of times, i have just gone myself and "followed the crowd" but then that brings challenges at passport control and baggage reclaim as you can imagine - but then you see the best of human kindness, and other passengers readily offer help - but it isn't fair to expect that at all.
Summary? I know that "assistance" is an additional service, but it has no flexibility to adjust to the individual circumstance, is executed very badly in terms of timeliness and then there is the somewhat defficient manners and language skills of those employed to consider.
I think it could be vastly improved, but where is the insentive. By paying (in the UK) airports to run the service, what are they going to do? Run it barebones, hope they get away with it and pocket the proffit of course.
Just a nod to the onboard experience here to complete the picture. My experience on my regular cariers, BA, Virgin and American - perfect, I have never had anything but brilliant service and assistance when i need it - so well done and thanks you guys...