A good dryer senses the moisture and adjusts the heat so it dosnt shrink your clothes and you dont have to take them out damp and hang them anyway, throws in a few reverse spins so clothes dry more evenly, and some other stuff Im sure.
It really depends, Ive stayed at hostels where the machines run 3+x a day and sometimes some machines will be 5+ years old. There doesnt seem to be any rhyme or reason as far as brand or usage pattern, though I've never seen an old combination unit.