My friends and I were having a conversation about bitcoins, and randomly the question popped into my head.. why did Stones of Jordan become the "currency" at one point in Diablo 2?
Diablo 2 had a barter economy, but gold itself was not valuable enough to trade for any high-end items (because there was a max amount you could carry). So the economy needed something that was more valuable to serve as a basis of comparison between the value of high-end items. That something needed to be small (so people could carry a number of them), valuable (so you didn't need 50 of them to equal a high-end item), and plentiful (so that you could get enough of them to trade for a high-end item) At times perfect gems were used, but even these were low enough in cost that it was hard to value high-end items. The Stone of Jordan became the default for several reasons
This was around patches 1.06 and 1.07, way before Uber Diablo was created as a way to try to siphon off the ridiculous number of Stone of Jordans that were in the economy. Later Blizzard took actions to remove the duplicates, causing the economy to look for alternative bases for the economy, eventually settling on high-end runes.
Here are some additional references
The biggest reasons SoJ became the defacto standard is the ease of duping pre 1.09. Those SoJs are typically called pre SoJs and can readily be identified by their lack of a level requirement. The key to this is because after 1.09, all uniques came with a UID of some kind, and if there were ever 2 UIDs of the same item in a game, one (or possibly both) will 'poof' and be deleted. There was a way to get around this issue since all pre SoJs did not have this UID feature, and one could dupe them on the classic servers and then port them over to the expansion servers where they get newly generated UIDs.
Also, SOJs are just plain useful, giving +2 to skills and a lot of mana. Other than the duped rings or occasionally the BK Band, most people today still use SoJs.