I call an 8x10 contact print 8x10, because 7-5/8 x 9-5/8 sounds awkward. I would expect that if the image were being sold at Christie's, the actual dimensions would be used, in part just to authenticate the print with regard to method of production and date. Same would go for a book such as a retrospective.
So, I don't think the terminology has anything to do with (dis)honesty in marketing, as most prints are not sold by the square inch. Of course, I would not call a print that measured less than 5x7 an 8x10.
Some people do print with big borders because the prints look much like they are matted, and this makes for a much lighter portfolio for carrying and mailing, as opposed to all the added weight of the mat board.