A watch is a mechanical marvel. It has gears and wheels, sliding parts, rotating parts, axles and spindles, synthetic jewels and bushings..
It just needs to be cleaned and oiled occassionally to function practically forever..
At some point, the metal-to-metal and pivot-to-jewel (say rock) wear is going to grind away the metal parts until nothing is left and it fails completley. It is going to happen....not might happen...but is going to happen..
I think that the guideline of 5 years is conservative and I will go 7 comfortably..
I also do not believe that you need to have this necessary cleaning and oiling done by an expensive RSC.. It can be done by any competent watchmaker for much less cost..