Betting odds are based on bets placed which does not always follow logic. The logic of gamblers if any logic at all - and one could say gambling at all is not logical (unless your are taking the bets rather than placing them).
I am well acquainted with the procedure. I suppose I should have written "I am a little curious as to why gamblers are putting more money on Murray than Federer" to avoid ambiguity.
The big money (%-wise) has yet to be placed, surely, we'll see how the odds develop over time.