For those of you who say they would hep someone who was struggling I do think that is a lovely thing. If I was limping along with shopping or a heavy bag and someone helped for a bit I would accept and be very grateful.
Advice for the helpful and concerned, if I may, would be to say 'are you in pain and can I help?' rather than saying the word limp, because pain really is the problem, not the limp, iyswim, and mentioning my limp always feels to me more like an observation or inquiry rather than concern.
Not that the comment that prompted the thread was that, it was just sheer nosiness. "Oh, I see that you limp..." 
I should perfect an answer that shames the nosy ones. "Yes I do, it's really painful, and I hate to be reminded of it because it cuts right to the core of how I see myself, whether I am whole and attractive and how it has crippled what should have been my youth" 
I usually just say "yes, isn't it glamorous!" 