We are isolating the static definition of the Outcome from the presence or absence of an amount wagered. Note that the Outcome is shared by the wheel's Bins, and the available betting spaces on the Table, possibly even the Player class. Also, if we have multiple Player, then we need to distinguish bets placed by the individual players.

Changing a field's value has an implication that the thing has changed state. In Roulette, there isn't any state change in the definition of an Outcome. However, when we look at Craps, we will see that changes in the game's state will enable and disable whole sets of Outcomes.

Yes, the money is anonymous. In a casino, the chips all look alike. However, the placement of the bet, really does have unique identity. A Bet is owned by a particular player, it lasts for a specific duration, it has a final outcome of won or lost. When we want to create summary statistics, we could do this by saving the individual Bet objects. We could update each Bet with a won or lost indicator, then we can total the wins and losses.

This points up another reason why we know a Bet is an object in its own right: it changes state. A bet that has been placed can change to a bet that was won or a bet that was lost.