That poster has been there ages, but it's not necessarily in a place you'd notice when returning to the station when it's busy. Maybe they moved it? (It was on the wall behind the wide access gate if you're looking in from the platform (2/3, or 12b or whatever it might be when the displays are cocked up as they always seem to be when I go there).
I am not sure why it's taken so long, and while receipts are arguably poorly designed, that's what people need if they wish to make an expenses claim. I can't imagine there being any need to keep a ticket. If you had Plus Bus, that would be a separate ticket anyway.
But, for most people, it's far more sensible to use Oyster from there now anyway? Anyone travelling off-peak should definitely use it, assuming you're heading London bound.