It is insulting because obviosuly you would have to be a real dumbass to buy an N-Gage. That makes this basically the modern form of "You bought a Sega 32X, didn't you?"
Bill: You bought an N-Gage didn't you?
Luke: Terence, wheres you kitchen?
Terence: Right over there luke!
*Luke gets lost in the basement*
Terence: Luke! You moron! Your in the basement!?
Mr.Harris: Luke bought an N-Gage didn't he?