You have missed nothing. It is just another traditional business implemented "on blockchain", and as usual the blockchain here doesn't add value.
In Augur you buy shares of an outcome, and the value of those shares can change day to day, and you can sell at any time. Whereas with a bookie, you bet on the outcome with fixed odds. Bookie lines may shift, but your bet will be locked in and unable to appreciate in value.
I'm not sure why bookies haven't implemented this share model, maybe its needlessly complicated.