the way i think of it is this.
say you're buying all kinds of climbing gear to climb el capitan. you're spending tons of money on rope, harnesses, cams, nuts, biners & webbing, rock shoes, tape, etc. etc.
the guy at the store offers an extra climbing rope but you decline.
then you're up on the wall. it's your 7th or 8th pitch, so you're roughly 450 meters up, and by some weird freak accident, a bolt of lightning hits your rope and tears it in two (or a rabid squirrel chews through the rope).
so now what do you do? you have to get a rescue team to grab you off the cliff, and for the sake of argument, say that you have to pay for this rescue service which ends up costing far more than that extra rope would have ever cost.
now don't you wish you had bought that extra rope?
but then again, if you climb all of el cap without any incident, then the applecare...er...extra rope would have been a waste of money.
(hopefully all that made at least a little sense)