A few thoughts:
a) the Earth rebellion may have been led or inspired by Omoroca ("Fire and Water"), and so may have had outside knowledge to know that buying with a coverstone would be necessary/appropriate
b) we wouldn't be able to connect to a buried gate, so we're unlikely to have been to such a planet - there're very few we've been to apart from by Stargate
c) the Goa'uld seem to have just abandoned many planets - e.g. "First Commandment", "Brief Candle" to just begin thinking... so they may not have need bothered put up coverstones
d) the coverstone was a dodgy plot device in the film - if Ra had really wanted to re-enslave the people of Earth at Giza he could have done so by force from his pyramid ship; but it has provided a useful technical widget in SG-1 for allowing peoples to keep their gates "closed"
e) being buried needed require a coverstone - that's a particularly Egyptian trait (perhaps), and other cultures may have used other things - burial mounds, temples, sealing it in a box etc... but see (b)