Great post. Derrida's idea of differance plays on the French for "difference" and "to defer"; he argues that differance is the nature of making sense (ie, what he calls "writing") itself. So no one lives outside of differance, just as no one lives "inside" it either. :)
The problem is that, as with the example of the person in the wheelchair, people don't generally recognize differance--ie all the ways that buildings, sidewalks, the entire built environment do, but might not, confirm their assumptions about what's what--until somebody puts difference (with an e) up in their face. At that point, you only get (reified) difference--which of course has its uses. You don't get the juice of the idea, which is that even differences differ and defer in meaning. (Cf. Mahadyamika school of buddhist philosophy, in re: experience of emptiness; or, the Matrix in re: "There is no spoon.")
Christian