FWIW, OSM lists both my and my neighbors' long driveways as "service roads." (Which isn't an obviously incorrect classification although the actual mapping doesn't seem wholly accurate.)
The proper way to map a private driveway in OSM is `highway=service,service=driveway,access=private`. I can see why you, or a simplistic data consumer, would class that as “service road”
So, as I read it above and in the Wiki, I gather that driveway is a subset of service road? (Actually, in my specific case, it's a little more complicated in that the access to a couple houses and a couple outbuildings are interconnected so it should probably be tagged 'driveway=pipestem' as well.)
Refinement is probably a better word than subset, because it depends on how the data gets used; if someone makes a map that interprets all highway=service the same way, driveways will look just like all the rest. If they interpret service=driveway in addition to highway=service, then they will look different.
