It is insulting because obviosuly you would have to be a real dumbass to buy an iPad. That makes this basically the modern form of "You bought an N-Gage, didn't you?"
Carl: You bought an iPad, didn't you?
Kyle: Stan, where's the kitchen?
Stan: Right over there Kyle!
*Kyle gets lost in the basement*
Stan: Kyle! You moron! Are you in the basement!?
Eric: Kyle bought an iPad didn't he?