It's not just the price of duels, its the fact that they are:
1. Generally unavailable
2. Cannot be used in other formats (bar legacy)
We have this discussion here is Aussie all the time, and i'm a keen advocate of increasing the proxy count (currently @ 5) but people still complain about card availability, and not just moxen and semi power, simple stuff like FoW's, wastelands can be issues, becasue they invest in cards that cannot be use in PTQ tournaments. Price is a lesser issue.
I agree with coyoteuglly's points also.
Haven't read your article Steve (no premium) but good job anyways

Can't comment on Aussie but in the US duals are pretty easy to find. Sure not everyone has a set of trops in their tade binder but stores that carry older stuff have duals and they are all over ebay/online stores.