Yeah the big problem is with things like your 80,000km service, which includes timing belt, water pump etc which if not gone can completely blow up your engine. So if your car has really done 100,000km, but you think has only done 25,000km, by the time you hit the "80,000km" mark you have really done 155,000km and your engine will have gone KABOOM due to a busted timing belt by then.
Also things like I am experiencing at the moment with my R34 at 160,000km like every second week having a heater hose leak, also the heater core has leaked and been replaced (requires whole dash removal) ..... so instead of those things being many, many years away, if you have bought a lemon with already 100,000km on it, then you don't have long before things start going wrong big time ....