Assets have their basis marked-to-market upon death, because they are then taxed as part of the estate. It would rock if I could pass along assets to my kid through the estate at their basis... You probably won't like what that produces though.
There are some other practical reasons for marking assets to market (for instance, determining the basis of a stock my aunt held for 60+ years is a bit tricky now that she's dead...), of course. A simple investigation of the matter would turn up a bunch.