I hate to differ with you, QB737, but the correct phrase ought to be, 'They should pre-board you.' Unfortunately, I've seen special-needs passengers brought onto an airplane in the middle of boarding or at the end (with a seat in the very back, no doubt). Of course, my airline's (EV) policy is to pre-board all special needs passengers, however, the vast majority of our gate personnel are not sensitive to the needs of our passengers (or simply too obtuse to even notice special needs).
When boarding, my approach varies when it comes to special needs passengers. Many people are fiercely independent and take any sign of lending help as a direct insult as to their abilities. Others b*tch up a storm if you're half a second late in offering a hand. For me, it's really a game of observation and intuition. I generally act of the side of caution and at least offer to help. If they refuse, then I stand back, ever watchful, and let them tackle the stairs themselves. Often times, I'll joke with the senior citizens that 'it's half the trip just getting up those blasted stairs, eh?' to which they often giggle.
Ignorantia juris neminem excusat.