It's not even the stores that mix-match capacities of machines........
too many times people buy or replace a washer or dryer without consideration of its counter part at home, I don't think I have ever seen a small capacity washer teamed up to a large capacity dryer, its always the other way around....
and people always think when a salesman ask them what size dryer they have at home when buying a washer, that its a sales gimmick to buy both.....their only tying to solve a potential problem......
but yes it s true about machines fitting in doorways.......I have a matched SQ from the 70's, but the dryer is too wide to fit down the basement stairwell, so it sits alone in the garage, I am contemplating taking it apart, and then reassemble it once in the basement....