Tumble dryer

In the rented flat in Mavisbank Gardens where I lived for the first three years in Scotland, there was a washer/dryer. And when I needed a new washing machine for Rose Street, I bought a washer/dryer. Both were fairly crap at drying clothes, but I thought that was the best you could get without going for the big industrial tumble dryers found in laundrettes.

Imagine therefore my surprise when Phyllis talked me into buying a real tumble dryer at 200 quid and it turned out to dry a whole washing-machine-full of washing in an hour with ease! Furthermore, the clothes come out almost non-creasy.

So why is it that people buy washer/dryers, except for very small flats where there is no alternative? Do people just na?vely assume (like I did) that washer/dryers will do the same work as separate washing machines and tumble dryers?