Why B Major?
Scale that fits the hand most naturally aiui.
m1469, why not just transcribe a beginner piece that isn't in B major? [edit: doh, like you said in your post anyway I'll read it next time ]
It is difficult for a beginner to read a piece in B Major because of the 5 sharps. That's why all methods start with C Major. It's a matter of music reading.
Well, I think that is very psychological. If they have no preconcieved notions about what is difficult and what is not as far as reading music goes, there is no reason it would initially look any more difficult in B Major than in C Major (as far as the notes within the staff).