I'm not sure if I understand question #1 correctly, but if I do, we call it "grading on the curve" in the US. That would be relative grading -- setting the grading scale so that each student's assessment is scored relative to those of the other students.
As for #2, there is indeed a difference between wish and hope and the two are seldom interchangeable. In the example given, the correct choice is hope. However, you can say, "I wish you a Merry Christmas." In fact, a popular Christmas carol bears that sentence as a title (except it's we instead of I). Here, wish is used as the main verb, and bestows a greeting or good thoughts (wishes) upon someone.
Hope is typically used for possible, real situations -- used to express a particular desire or outcome for a future situation. (I hope I do well on my test tomorrow!)
Conversely, wish is usually used for imaginary, unreal, or past situations in which the outcome cannot be changed. We often use wish in second and third conditionals. It can also be used with a past perfect verb to express regret that a desired outcome was not realized. (I wish I had done well on my test yesterday!)
The concepts of wish and hope are related, but the words are used differently.