I've had maybe 1 in 4 of my cameras serviced.
Before you start worrying though, NONE of them were the electronic picture makers, all the ones that required a service (normally referred to as a CLA - Clean, Lubricate & Adjust) were film cameras, and the newest one that needed a look at was the Canon A1 which was produced in 1979 according to it's serial number. And even that one was really a Lube job for a known issue with the mirror damper mechanism (the "canon cough"). The Fed 3a from 1969 needed attention to the roller shutter because it had begun to lose it's rubberised coating and was basically not light tight anymore, and the Voigtlander Perkeo I from around 1956 needed the shutter mechanism cleaning from the old oil/grease that had set through old age and lack of use. Strangely, the oldest camera I've currently got, a Kodak Autographic from 1915-ish (bits are from 1915, other bits from 1920...) basically "just works" so it's not a given that it's just down to age either...
Basically, I reckon that apart from a reasonably regular clean of the sensor, and with "normal usage" you're unlikely to need to actually service a digital camera before it's basically so obsolete you've stopped using it 5 years before...