Can someone describe in detail how "auto-set" clocks work?
I'm led to believe that the people telling you it really is just a battery-backed clock are correct. If you figure that from factory to purchase at retail is no more than, say, a year and it's acceptable to drift, say, 5 minutes in that year, that's an accuracy of ~9.5ppm which is -- these days -- not at all difficult or expensive to get out of a temperature-compensated crystal oscillator. (For reference, many cell phones typically use ~2.5ppm oscillators, and in large quantities the price is somewhat under a buck.)
---Joel