@Soulfox -- that is only true if you are dealing with a tape deck that has a belt. A lot of them (I don't know the percentage) are of the direct drive variety and don't use belts. In fact, the better tape decks are direct drive.
On the subject of belts, it is fairly easy to tell if you have one. Those generally stretch over time, so if the tape deck's speed is noticeably off the chances are good you have one with a belt in it.