As there years pass I use ESC . daily hoping that it will get the last chunk of the previous line on my screen, despite any ^P's or ^R's I might have done.
Never have I wanted it to consider those ^P's and ^R's. So even though you said that was a early design choice, perhaps you could still leave (behind for posterity) a toggle variable or new binding to do my dumber mode. My http://www.useit.com/alertbox/ style survey of many years with hundreds of hours with, er, 1 user, "indicates", as they say in the medical business, that this is needed. Surely you (all) are not such constant hammerers of ESC . as I. Vote for Choice.
