It makes perfect sense to me why these dupes aren't so widespread that the AH is flooded with them. I think people are severely underestimating the intelligence of these dupers.
1) If you were duping BiS items and then selling them on the AH for 2b gold to cash out (which is far more profitable than selling on the RMAH for $250 currently), you would be a complete idiot to put more than 1 of these items on the AH at a time. 2b items that are actually worth their price are tracked and multiple copies of the same item on the AH/RMAH would discourage legit players from buying them (would you buy an item knowing it was a dupe?). In fact, to be safe you wouldn't put duped items consecutively on the AH because it might drum up attention.
2) 2b items do not insta-sell, in fact the more expensive the item the longer it takes to sell usually. People who have this kind of gold track the same items sometimes for days. Think about it, if you're literally dropping nearly $1000 on an item, you'd better make sure it's worth the price. If we estimate it takes ~3-4 days to sell one of these 2b items on the AH then 10 of these items existing on diabloprogress means the duped item in question has been on the market for over 1 month.
3) It's very difficult to differentiate the method of duping (whether it's rollback dupes or some actual in-game technique). You'd think we could keep track of a couple of these duped items and see if their quantity increase over time (which would be a tell-tale sign that it was some in-game technique) . Unfortunately the dupers know that we can keep track of the quantity of these items so it's unlikely for them to keep selling the same items (especially since people who actually have the gold to buy these items will be discouraged knowing it's a duped item). The most we can do at this point is to keep tracking items to see if more dupes pop up. If more duped items keep popping up and their quantity is 5+ we'll know it's unlikely that they're all from roll-back dupes.
You can bet the people who are duping already had a ton of gold to begin with (hence how they could acquire such good items to dupe) and know how the AH works at that level. Therefore they would take the proper precautions to minimalize their chances of being caught or their trail being followed.