There are a few things that have been missed here
Firstly, an 18 inch "Slimline" dishwasher is not normal size here, most dishwashers are 60cm (24in) wide as in America, the slimline models are for kitchens where space is a premium.
Secondly, most people do not have "undercounter" Fridges here, most have either 1 undercounter fridge and 1 undercounter freezer, or a fridge freezer, which is an under counter fridge and an undercounter freezer mounted on top of each other in a single cabinet.
Also, although Europeam washers are smaller than the standard American machine, as has been discussed in length on here, they are designed so that they can be filled full to capacity, whereas most american machines are designed to be loosely loaded 1/2 to 3/4 full at best. This means that European machines basically wash as much, or almost as much, as a typical American machine, making the larger size pretty pointless IMO.
So in reality, most European appliances aen't really that much smaller than their American counterparts, they just fit into smaller spaces better.
Matt