I decided to run this past my dad, who has owned a small chain of ASE certified independant repair shops for 25 years. He's not a technician, but he's gotten pretty good over the years...
I lost the text of our conversation via IM, but basically he said that it would be very unusual to have JUST plugs go bad at 30K miles without something else being wrong. For example, if the car was for some reason running very lean (not enough fuel) and then driven hard for an extended period, that could damage the plugs.
He suggested asking for the used plugs. Assuming it's an ethical Service Department, that should tell you a great deal. (Almost certainly you can find pictures on the web to look compare to yours for every imaginable condition in which plugs are found...)
Having JUST the plugs go "bad" @ 30K would be very unlikely, and would seem to be MUCH more likely to be a "service opportunity" for the stealership... We'll see! If everybody starts having Check Engine lights come on @ 30K with nothing else wrong, that will be pretty telling!