@maporsche,
This is how to think of it. You imagine the bookie's bag at any point in the skirmishes. The book is where transactions are recorded. A perfectly round book is one which has $100 in it and each result takes $100 out of it. Something akin to a non-profit organisation if you appreciate irony.
In this instance we have $55.55 to be bet on Chicago to take out $100. $34.77 to be bet on Rio to take out $100 and $6.66 on Tokyo and Madrid each. Which adds up to $103.64. In such an ideal, rarely achieved, the bookie wins $3.64 with any result. His book is said to be 103.64 "over round". Which is actually very generous as bookies need a margin to pay overheads and keep their lady friends in the manner appropriate to their station. But if the market is large it is sometimes enough. $1million in the bag gives a profit of $3,640. Which is still low. i.e. generous to punters.
We get 107 over rounds at big race meetings where there is a very active market such as Royal Ascot but 115 to 125 is more common with lower turnovers.
It is important to consider that the punter has the choice and may be privvy to "information". At any point the bookie may not want to "lay" one or more of the runners and want to "get" others to steady his book. In which case he holds the prices of the former at levels below his competitors and raises the prices of the latter above them. If he was overloaded on Chicago he would offer 2-1 Rio for example. Or maybe reduce Chicago to 4/6.
It is a dynamic situation. At dog and horse race mettings a great deal of activity takes place in not many minutes. It will be more liesurely in this Olympic venue market.
And some bookies like gambling themselves and are prepared to go against a runner. We call it his "Bismark". If one bookie, who had, say, a friend who was connected to the Olympic Comittee, decided that Chicago wasn't capable of accomodating the committee members in the style they have come to expect, he might offer 10/11 Chigago and take most of the bets on Chicago as a result of the calculating greed of the punters who are just as human as bookies in that regard.
I have heard a rumour that all is not well with the Chicago bid. Whether that is the case or whether somebody is trying to get better odds by putting out rumours is a matter for each of us to judge.
And it is a simple fact that if bookies don't make a profit there are no bookies and half the fun would go out of life. In general bookies take less out of the punters than the machine does. They are less scientific. Less communistic.
Beware of "Ladies Days" at racecourses. On such days there is a large crowd of innocents and the bookies will take advantage by raising their over-round to 140 or even 150. In which case seasoned gamblers retire to the bar and bet amongst themselves.
I would make Chicago my Bismark. The IOC are a world unto themselves. Stories about foreign dignitaries being arrested face down on the pavement in cuffs and being paddied off to the station to be photographed and whatnot for crossing the street without permission are hardly positive inducements.
