Numbers are in the vague ballpark.
C152 = 159.5 sq feet
C172 = 174 sq feet
C182 = 174 sq feet
For the C120/140, don't know the square footage, but the book says it's the same airplane, one without flaps, so the wing area would be the same.
Perhaps the original naming trend had its origin as the square footage, but it since became just a marketing thing, since they haven't followed the pattern very closely.