Delta Upgrade Priority

For years I have wondered how the airlines determine the priority on the standby lists, most specifically for 'at airport' upgrades. Delta, on their slick plasma/LCD screens at the gate, have a message (roughly) saying "your position on the standby list is influenced by your SkyMiles status and the cost of your ticket". Last year I was able to significantly exceed the Platinum qualification threshold, almost double, so was hoping for more frequent upgrades this year. My experience to date is not good, so I am deducing that the statement above should read "your position on the standby list is influenced by the cost of your ticket (first) and your SkyMiles status (second). Either that, or, on the flights that I have been using, there have been an awful lot of Plantinum Elites who also exceed the threshold by double or more. Not impossible, but 10-15 on each flight? If that is true, more power to Delta, they must have sold a lot of tickets last year.