Is there really that big a difference? Maybe in terms of abuse they can take as in banging up derailers when locked up, etc. But I don't find there to be much in they way of maintenance for a derailer, some fine adjustment once in a while, just like watching tire pressure and an overhaul every year or two.

Fixies can really wear out BB and rear hub bearings as well as they get more abuse than on a freewheel bike.

Al