Ask Mr. Smarty Plants

In general, you want to disturb the roots of your trees as little as possible.  Since a large percentage of a tree's feeder roots can be found in the top few inches of soil, any removal of that soil is bound to disturb those roots and adversely affect the tree.  Relatively few of those roots are located near the base of the trees, but are usually concentrated near the tree's drip line.  Removing soil all the way to the drip line seems excessive, but there may be reasons for the recommendation that are not apparent to us.

In fairness, soil around the crown of a tree can cause problems.  If your soil has a high clay content, which restricts oxygen exchange to the roots, the problem can be very serious, indeed.  Some tree species are more susceptible than others to problems caused by deep planting.

The answer to your question is not cut and dried.  I would tend to follow the advice of a certified arborist, but if you have doubts, you might hire another certified arborist on a strictly consulting basis (there will be no financial advantage to give you advice one way or the other) and get a second opinion.  That involves more expense, but your landscape trees are almost always worth the expense of maintaining their good health.