[mattlondon]

This.

Everyone remembers being told at school from a very early age to "cross out" things you dont want any more (such as writing the wrong word/spelling, getting the sum wrong etc). At least in western cultures anyway, this seems fairly universal.

Seems to me to be a very easy semantic jump to go from "disregard this mistake" on paper to "disregard this thing I am looking at" on computer screens.