Rotor and pad life can change quite a bit...
I would expect that pad change at 30k is normal, I've seen people with badly worn rotors at 30k also. The system and materials are designed so that the pads are worn and changed while rotors do not wear out so much. Apart from driving habits, rust and badly worn pads are enemies of rotors (by scoring them).<br>
One thing though, to my experience one can tell by looking or touching the rotor that it needs to be replaced. The brake pad does not touch all of the rotors face hence the parts of the rotor that do not touch the pad (e.g. the outside periphery) is left high, not-worn, so this can be seen or felt by hand (or at least measured by a micrometer) since the edge created between the two zones is quite distinct. Some mechanics even apply the practice of honing down the rotor flat up to a certain small limit to smooth out the face, but this is obviously not reccommended practice by the factory, and could be a safety hazard.<br>
To be on the safe side I would change pads before they are totally worn out and the steel backing very quickly scores the rotors which are expensive. I do not rely too much on the brake-lining worn out tell-tale light, although theoretically this should protect the rotors, the pads may be in such a shape to damage the rotors before this sensor is activated.