SC-Usual

Ex: A mercedes is more expensive than usual for a car --> wrong
A mercedes is more expensive than is usual for a car --> sounds better

Warren Buffet is richer than usual for a human being --> wrong
Warren Buffet is richer than is usual for a human being --> sounds better

I believe the difference between the 2 is that the former is equivalent to normal and you usually intends "compared to the subject's self"
Ex: He is nicer than usual --> ok

The latter "is usual" is used to compare the subject, being part of a subgroup, to the overall group as shown in my examples.