Disabilities, Difficulties and Differences

Hoooo-kay.
Ever heard someone trying to be politically correct refer to someone using walking aides as "Differently Abled"? Or a school refer to the kid who needs a helper sitting next to him as having "Learning Differences"?

I'm going to start here with a few dictionary definitions:

Difference:
an instance or point of unlikeness or dissimilarity
a change in, or effect on a situation
a distinguishing characteristic; distinctive quality, feature, etc.
the degree to which one person or thing differs from another.

Difficulty:
task, problem, etc, that is hard to deal with
a troublesome or embarrassing situation
an objection or obstacle
a trouble, or source of trouble; worry
lack of ease; awkwardness

Disability:
lack of adequate power, strength, or physical ability; incapacity.
a physical or mental handicap, especially one that prevents a person from living a full, normal life or from holding a gainful job.
anything that puts one at a disadvantage

So by these definitions, my dyspraxia causes Differences in the way I learn new things best, and Difficulties in dealing with new social situations, certain types of interactions (interviews, phone calls etc) and probably doesn't cause any outright Disabilites. With HMS, I have Differences in certain ways I'm able to move (I'm pretty flexible, not surprisingly) and see (I get double vision almost all the time), Difficulties in other areas of mobility (I can't walk for long periods of time, especially on bad days, stairs hurt my knees and hips... etc)

I wouldn't classify myself as Disabled, in general. I get up most days and go to a (volunteer) job, I go out some nights, I have physically active hobbies (which are almost all actually pretty social in nature too) and generally on the surface don't appear to be outright unable to do things. That doesn't mean they aren't hard. Half the time, the effort that goes into standing up straight and smiling at every customer in an afternoon at the shop means I go home, cuddle up in bed with the laptop and am done for the day. On a really bad day, I might feel Disabled. Everything hurts, I have the attention span of a gnat and the emotional maturity of a cocker spaniel. That doesn't make me Disabled all the time though. Yes, I'm affected by my Differences and Difficulties all the time, but the extent to which each of them is causing problems varies.

But where do you draw the line? I know someone who uses a wheelchair most of the time, who can get up and walk for a short distance occasionally, but certainly couldn't every day, or for long enough to keep up with the "normal" world. And I know plenty of people (I'm one) who sometimes use a walking stick, trekking pole or crutch to help get around, especially at the end of a long day. For me, I can go without, but the amount of pain relief I get from taking a little of the pressure off my knee means with it I can stay out longer, enjoy myself more and keep up better with those of my friends without these... now which D word do I want here?