Brakes: front end wobbles when braking

The front disc brakes on my 2002 GMC Safari wore out after about 38,000 miles so I replace them with new NAPA Ceramix disc brakes. After installing them, every time I applied the brakes the front end would start wobbling - steering wheel wobbled - but the van would stop. I took the calipers off and removed the rotors only to find out that the inside surface of the rotors had all these surface imperfections, like air bubbles in the steel when the rotors were cast. I replaced them and reinstalled the Ceramix disc brakes. The van stops fine now. I make it a part of every brake job to take the rotors off and inspect the inside as well as the outside surfaces from now on.

Rob