There are regulator components that need to be replaced based on
wear. This includes, well, all of the components typically replaced during annual service.... But in many cases the o-rings and seats and diaphragms are
not anyway near the end of their service lives after 1 or 2 years, but the service manual calls for replacement of all parts contained in the service kit, no matter what.
This is not bad mechanical practice, considering the regulator has been completely taken apart and the replacement parts are so inexpensive.... But just because most of the internal "soft parts" are changed during service does not mean that replacment was actually
necessary at the 1 or 2-year mark.
Many of us have serviced regs that are 20 - 30 years old, and found o-rings that were still soft and supple.... they were not at the end of their service life. And on the other end of a the spectrum, I had to replace a HP seat with less than 2 years use on it.
So the time period (every year, every other year) is arbitrary, but is the only way the regulator companies have to ensure that their regulators see somewhat "regular" service. Most divers have not learned to correctly inspect and test their equipment, and so the annual service builds in a "safety margin" to help catch problems that the diver does not know how to recognize on their own...
I do think we divers should be taught more about our equipment.... removing some of the mystery will not stifle sales, but will improve safety.... sorry, I'll get off my soapbox now
Best wishes.