Mate, I have heard of a 20 year old set which has been serviced ONCE in that whole time... And if vollies make a fuss, they believe they may risk loosing it....
To your Q tho, I would say the onus is probably on the brigade. At the end of the day you know how much it is used, how regularly, to what extent, what conditions it is exposed to... etc etc... I would say for a set which is used regularly annual maintenance / servicing wouldn't be a bad idead... For the tools any way.. The pumps, with weekly brigade checks should be able to last a little longer.
Just remember, the better the gear is maintained, the easier and "safer" it is to use at a job.