I don't think the snakes care either way if the rodent is live or dead. There are a couple of reasons it may seem that they prefer live. One being that the rodent may not be prepared properly therefore the snake does not recognize it as a food item. The other, being that Bp's are very timid snakes and I believe the human presence involved when feeding F/T will cause some snakes not to go for it. This would explain why many times people have success just leaving a f/t rodent in the cage. Look at almost any other species of commonly kept snake that aren't as timid as Bp's and there aren't often problems feeding f/t. If snakes truly preferred live, then there would be no market for frozen rodents.
Not advocating one way or the other, I just think it's a bit silly to say that all snakes prefer live food. There are a few things that tell a snake that something is edible,
Scent
Movement
Heat signature (in the case of most pythons)
Being ambush hunters I don't think that most snakes really hesitate when a food item comes near them. If it's warm, moving, and smells like food, they are driven by instinct to eat it. There is a reason they are called opportunistic hunters.
Gain some experience feeding some other species of python and you'll find that a lot of them will have the rodent wrapped up before they discern whether or not it is live or dead.
Of course I could be completely wrong about all of this.