My 1998 Honda Accord was still under warranty when I took it in a few months ago for regular maintenance. The Check Engine light was also on, but that's pretty much a catch-all idiot signal and it usually means there's a problem with the emissions system. The helpful samaritans at the dealership decided it was on because I needed a new catalytic converter (NOT covered by the warranty, btw) to the tune of $1,000 for parts and labor.
I checked out some Honda chat rooms and found out that this is a common "suggestion" even though the expected lifespan of a Honda CC is at least 100,000 miles and the car's emissions system has a learning curve that allows it to adjust to an imperfect, but still perfectly functional, converter.
I decided not to get the CC replaced, my car made the adjustment and everything's fine.
But it made me wonder how many people blindly plop down a grand because they don't know what the light means, how their car's emissions control system works, or that you're allowed to disbelieve a dealership mechanic. Sad.