I don't think it's quite the same. To me, there's just something "off" about big fees around testing. I'm okay with an instructor charging a bit if they are doing some of the testing outside class time. I'm even okay with them charging a bit for the bother of it all. But when "a bit" gets into the $100's, that starts to bother me. Why should the year you are testing cost you 150-200% as much as the year before? I also think it can create a reason for students to delay and resist promotions, which starts to break down whatever meaning the ranks are meant to carry.In the end, you're paying for both, it's just how many checks you write to get there.
As long as it's not "pay me $400 and you will guaranteed get your belt" or "pay your tuition fees and show up to class and you'll get your black belt" I don't see the problem with it.
Mind you, it is entirely possible to charge $100's with a clean conscience, good intentions, and a good outcome. My reaction is gut-level, and not entirely logical.