Thanks, yes! I.e. who is this "everyone else," and where do they treat it the same way Jaynes does? I'm not aware of any examples, but I have only a basic knowledge of probability theory.

It's certainly possible that this approach is common, but Jaynes wasn't ignorant, and he seemed to think it was a new and unusual and maybe controversial idea, so I kind of doubt it.

Also, I should say that I have no dog in this fight at all; I'm not advocating "Jaynes is the greatest thing since sliced bread", for example. (Although that does seem to be the opinion of some LW writers.)