Most RTCs do use the same crystals that are in wristwatches, which is actually the source of their error.

The tuning fork crystal design used in wrist watches has a parabolic temperature coefficient, which means that the clock is only really accurate at room temperature. This isn't a problem for wristwatches, because, presumably your wrist is at approximately room temperature, but it does become a problem for electronics that operate with large temperature swings. (like the inside of a phone or computer, for instance).

https://www.maximintegrated.com/en/app-notes/index.mvp/id/58