I am not sure what used to be, but as far as I can remember Boson has allowed for 2 testing modes. Study and Simulation. Simulation is times and study is not.
What your paying 80$ more for is the Boson Study mode and end exam break down.
The Study mode allows for people to quickly access resources and explainations for the questions a person is having trouble with.
The Exam break down helps identify the "types" of questions that you are missing.
I agree that if a person is ready to pass the real CCNA exam that the 20USD for mypowerpass is a much better purchase, but if a person is ready to pass the exam then they are really just using mypowerpass to raise their confidence.
Most people who are still working on the fundamentals or who have already failed the CCNA the extra money for Boson pays for itself by helping people identify what they need to work on and then providing resources to address those types of questions.
I believe that it really boils down to how ready a person is at the time they start looking at these types of products. The more ready you are when you reach this point the less you need the product to do, and thus the price difference between the two is greatly different. The cost may also be a factor that prohibits someone from using boson products and in fairness the additional content they provide is available for free by cisco, but at the price that the tester has to go and find these resources themself.
Even though I am well above the CCNA testing level I still would and do use the Boson testing products because of these extra features. For me the time saved looking up the referenace material to better understand why I got a question wrong is well worth the extra money.