These exist: e.g. http://www.lgwasherdryer.com/

The first time I'd ever seen one of these things was in Dubai at a hotel/apartment. I'm surprised they aren't proliferating through Asia given the limited amount of space but I figure give it time.

Incidentally, the cost on these washer dryer combo's aren't excessively high... in fact probably just a relatively small premium above what a good washer or dryer cost.