OK Scot, I believe I see the problem here. You base your observations on bonsai trees, I base mine on actual VFTs. You say that "Both bonsai and VFTs respond the same way..the EXACT temperature is irrelevant.." THAT is the problem. You are assuming that bonsai and VFT actually do respond the same way. Why? Bonsai are trees. Trees have bark, hard trunks, limbs and leaves. VFTs do not have these things. Why should they react the same way?
Bonsai trees, being trees, are fed by sap flowing between the leaves and the body of the tree, and in reverse as the roots feed the leaves and limbs moisture. This is controlled by the flow of sap within the bark and interior of the tree. It makes sense that as long as the sap is flowing, the tree will continue to keep its leaves.. even well into winter. Thus you get your "January greenhouse bonsai". It also makes sense that as long as the sap is frozen inside the tree it will not "break" its dormancy untill the sap begins to flow in the spring. This is why your trees break dormancy "2 weeks later" when it got warmer. In essence, you are correct. When it comes to bonsai trees, and "regular" Western NY trees, its the temps that are the key triggers that initiate what we see as "dormancy".
VFTs do not react the same way as these trees do. They dont have bark, or sap. They dont expect to be frozen solid for several months through winter. They LIKE warm days and chilly nights in winter. The triggers are different. Why would a plant that never recieves a freezing temperature have a trigger that reacts to such "extreme" cold as 40*? Your plants survive the fridge dormancy method because of the adaptability of the species, your skill, and a little dose of just plain good fortune. The fact they do survive does not necessarily mean that is what they would truly "prefer". I wonder, if your plants would grow better if they were able to get a lighter dormancy on occasion. On a similar note, I bet that your bonsai tree would not fare well at all in a VFT bog in NC all winter.
Cheers
Steve