Whether or not you get your original bet back depends on what you are betting on. In most casino table games you do get your original bet back if you win something. However with the lottery, horse races, slot machines, and cake wheels you do not get your money back if you win. The rule of thumb is that if you need to activate a machine to make the bet then the bet itself is gone. The cake wheel is obviously an exception to this rule but that game is for the benefit of fun and charity (I won a cake at a fair in Fresno years ago by the way).
Losing the original bet is not necessarily bad. If they returned it they would just depress the paybacks to recoup the money. If the odds are expressed as "to one," then you get your original bet back if you win. If they are expressed as "for one," then you don't.