Considering youre the 'master auctioner' (a fact Im not really disputing), you should recognize that rarity is not the only determining factor for how expensive an item is in a given economy. PoD may be rarer than SF perhaps in number of them currently available, but realistically thats only because people left alot of their Shadowfangs unbound expecting this exact scenario to occur, aka the (relatively recent) price increase. Its not like you actually hear of Shadowfangs dropping anymore from Arugal any more than you hear about PoDs dropping from the end mobs in Ulda.
Regardless, the real point of course is supply and demand. Yes, I will concede that there are many more Shadowfangs available than PoDs. However, the problem with your analysis is thats the only part youre factoring in, youre not really taking the demand into the picture. There may be 10 times more Shadowfangs than PoDs in circulation, but demand is probably much more than 10 times in favor of a Shadowfang in comparison to a PoD for a variety of reasons.
First, there are just more classes/viable specs that a Shadowfang is BiS for than a PoD is. Rogue, Paladin, and Warrior uses Shadowfang extensively in the 19 bracket. For almost all of their 'ideal specs' those classes will have a Shadowfang. In addition, although there could be some debate about it, math has proven that 2x Shadowfang is BiS for rogues at 19.
In talking about PoD, while there may technically be the same number of classes that have a BiS setup involving a PoD (shaman, warrior, paladin), there are much more prominent specs for at least 2 of those classes in competitive 39 play. Shaman and Paladin have a variety of competitive setups that dont even want a PoD, and Warrior is a very viable choice for 39 FC (which obviously wouldnt be using a PoD)
Secondly, there is without a doubt a _much_ larger pool of players/SFs needed in the 19 bracket compared to 39s. I only speak for US play here, but from experience I can say that 39s on Nightfall are happy to get more than 1 game at a time. The days of having consistently more than 1 game going at a time could be over for 39 twinking in the US. However, for 19s when I log on I would typically queue up to get a message saying 'now entering warsong gulch 4' or something along those lines. Four games going at once hasnt been terribly uncommon in 19s, its just a much more active bracket overall.
Finally, theres the 'rogue' factor. Everyone knows that hunters and rogues are the most popular classes in practically every twink bracket for their ability to lolfaceroll people. This is true even in 19s where rogues generally are considered pretty weak in competitive situations. Rogues cant use a PoD, and not only can they of course use a SF, they need _two_ of them to truly be BiS. The importance of this point cant be ignored.
