What do you guys think of the car service schedules, so many of you adhere to them?

I been told that maybe per year $2,500 PA is for car costs this may include the tyres and the WOF averaged out for the average motorist PA excluding maybe the insurance, regro etc. 

Over the years we have been getting cars from Turners given the hassles with dealers so we juts do away without the warranty.  We've never did the service schedules, the $8,000 car seems to last 10yrs when it depreciates to maybe $2,000 and we get another used vehicle at Turners.  Is there much justification spending $2,500 PA when one could spend just $400 PA averaged out?  That would be the DIY oils and filters and tyres, brakes when requested by our mechanic. 

One car we had from 2010 we did maybe 8,000km per year, (they're retired now so more like 3.000 now) we've had one set of new tyres, fluids, filters, a few bulbs and one electric fuse, the original (used) battery still going.  In a year or two may need a new one and/or some spark plugs.  Pretty much the same with a Mazda 323 we had for the 15yrs prior to 2010 when it was replaced.  That had the drive belt and the timing belt replaced and the muffler was repaired instead of a entire new one replaced, some CV joints, that was it really, was sold for $2,000  with a leaking water pump to a mechanic student. 

I admit it the fuel filter was never changed, ditto the trans oil / filter.  But on some Euro's the the trans and the fuel filter are not even part of the schedule anyway .... Ditto with injection unless one picks up the symptoms.  So why spend $2,500 PA when $400 would do, what am I missing?

Cheers all :)