I have a 2004 Toyota Sequoia with 85K miles. Should the timing belt be changed? Why?

You better believe there's a good reason. Most import engines are of the "interference" design. That means when the timing belt breaks, and it eventually will, the open valves will be hit by the moving pistons as they coast to a stop and they'll be bent. That turns a roughly $500.00 job into a $2500.00 job including new head gaskets and a valve job. Your dealer is looking out for your best interest by warning you to get this common maintenance item taken care of. You'll also find all kinds of related warnings in the owner's manual.

Honda used to recommend replacing the timing belt every 75,000 miles, and they typically broke at 65,000 miles resulting in very expensive repairs. Not all import engines are of the interference design but even those that aren't will leave you sitting on the side of the road in a pile of tears when they break.