When you place one of these bets for say 3 runners and those 2 come 1st 2nd 3rd do you get all 3 divs for your original investment?

Can't honestly tell you the real answer to that but I would imagine so otherwise it would be a rort.

Yeah, a few times I've boxed 3 or 4 horses in an any2 bet and they've come home 1-2-3. You DO get all 3 dividends, but you also feel a bit annoyed that you didn't take a box trifecta instead.