I can't help but feel that the list is a little dated where demand is concerned. Ever try a Yellow Tox tier swap? It generally won't happen due to low popularity. Yet other pets that aren't even on the list will be gladly valued at a mid Sept. or greater by most users (see August PPS Lion).
Now I am not trying to dis the list or all the work that has gone into it. However I must emphasize that making a list that factors demand as well as rarity will almost certainly mean pets will change tiers more often (even daily). Trying to stabilize the pets on an inexact rarity isn't going to completely gridlock the pet over popularity spikes. Yet we keep reading why they won't get moved..
I dunno. It just feels a bit biased. And that is even more obvious with staff pets. You won't ever see a Shima above any of its littermates because it is viewed as being disrespectful to the other staff. And coincidently all store pets and staff pets have a "fixed rarity". Even though we all know most store vr's are not actually vr, they keep it like that to sell more pets. Ask yourself why a 2010 VR is still a VR when compared to a 2013 newly brought "VR" store pet. As for staff variations, the rng system is never exact. So they shouldn't just change all evenly. Run some rng tests if you don't believe me.
You can give me many examples why such and such will not move. And I'll say that doing so just completely ignores current demand. Yes you can't change the list that often. But if people as a whole value something more, we should see some changes. And of course we can always fight demand by not bidding or trading.