When a room is booked for 2, the hotel has no way, in advance, of knowing who you're going to show up with. It could be your wife, husband, a family member, a hooker from down the street, or an imaginary girlfriend.

When traveling with my mother, we were "Mr. and Mrs. Eastbay1K" and one of the hotels had blocked us into a room with one bed (instead of the 2 requested), so any welcome would have been technically correct, but I suppose I could have been just as offended by the hotel not assuming that I could be traveling with my mother, who shares the last name, and the hotel would assume that we were married.

(We did not end up sleeping together!)