My '98 w210 is at ~43K miles and still has the original front pads. They are about 90% worn, but are still hanging in there. This car has generally seen suburban commuting, with a little bit of freeway thrown in, so it's not just highway miles. It didn't always have such a gentle life - it was the press car in MBNA's fleet used to introduce the turbodiesel to North America. So it got track tested by Car & Driver and some of the other trade rags.
I think your friend should get a new mechanic. If the same opinion holds, then he should teach his wife how to drive...