Does it stop people piling in at the death and effectively buying money?
Actually I believe it is the exact opposite.
I believe bookies pay out bets early primarily for publicity, and secondarily in the hope that punters will pile on all their winnings on something else before the season is out.
Im very surprised if its true bookies are paying out already as the odds are still only 1/3 1/4 ish. Usually, I would expect the odds to be at least 1/10 and more like 1/20 before the bookies start paying out.