The only time bookies lose is when they have badly calculated the odds for the bet.
On-course horse racing bookies generally come out on top whoever wins, apart from when the favourite wins, and very few people have betted on the other horses.
That’s why you get the 100-1 chance running quite regularly, they are trying to tempt people to bet on the longshot, as there is a lot of money going on the short priced runners, so thye want some money to offset it if the shorter price one wins.
I’d say football odds are far more sophisticated nowadys, as the bookies know at their head offcie immediately if someone has put £10 on Leicester etc. They will then quickly lower the odds on Leicester, as well as raising the pirce of Arsenal etc, to make sure they will not lose out whoever wins.
I’d go as far as to say the bookies will make more money this year if Leicester win, due to the sheer number of £10 bets on Man C, Man U, Arsenal etc to win the league.
It is in their interest to promote the amount that a few people will win if Leicester win, but if say, Man City had won, they wouldnt be promoting the 20000 people who have bet £5 on them winning – the amount they pay-out will be roughly similar, but spread over more people, and the bookies will still be making money.