It depends, of course, on what kinds of things you are trying to learn. And that is precisely what is at stake here.
You definitely don't go to the classics to learn science or technology. But is that all there is that is worth knowing?
And don't be too hasty in your division of "fields that make progress" and "fields that don't." Our knowledge of Ancient Greece, for example, has grown substantially in the past century, and there has definitely been progress in historiography--but that does not eliminate the need (or, more to the point, the desirability) to read the primary texts.