What's great about the mountain bike, is the evolution of parts that made its way to road bikes. Campy BBs, had no dust cover. You put grease on the ball bearing ring and screw on the cups. Early mountain bikes BB were same technology. Until they started using sealed bearings. I thought "wow!, i don't have to overhaul them every month!". So I bought Phil Wood hubs (sealed bearings) so I never have to worry.
Now, everything is sealed which is great. I haven't taken apart a hub or a BB or a headset for repacking in ages.
So I think most parts are quite interchangeable.
I love the MTB stem technology made its way to road bikes. Its a darn pain to change those quill stems without taking apart the brakes and tape.