I wonder that too. I have met a couple never bathed dogs who really do not have an odor at all, but most of the people I meet with dogs who proudly state they've never bathed them have dogs who are just gross. They're like petting an oil slick and they smell so overwhelmingly doggy.
And I don't think it's that smooth coated dogs smell worse than long coated dogs. I think it's that a lot of smooth coated dog owners never bathe their dogs, whereas most long coated dog owners do.
I think the worst smelling dogs I come across are generally retrievers, Malamutes, Sibes, Rottweilers and mastiff type breeds. I've met my fair shair of stinky Dobes too. I bet it is difficult to fit a giant breed into a bath tub, so I guess I can sort of understand that (although there are do it yourself dog wash places), but it's like a lot of people who own these particular breeds just don't believe dogs need baths.
In any case, I too like to make sure my home and my dogs smell as least doggy as possible. I like petting clean, silky, smooth fur. I don't want a film on my hands after touching a dog, and if I feel that film, I know it must be all over the rest of the house too. Ripley gets really greasy quickly, and smells like old feet or something after a couple weeks. It's really gross, and I don't know why het gets like that. I've thought about diet, but he is fed a good food, and I can't really switch him since he's so sensitive. So instead, I just bathe him every couple of weeks, keep the dog bedding super clean, wipe out his crate constantly, etc. I can't stand doggy odour.