The classics have their place as art and as sources of prestige, but if you're looking to learn things there are usually better places to look.
Not that I disagree with everything Mr. Sanger said, but the truth is a complicated beast.
 Some people studying the history of science read the originals, but thats different.
I would take issue with that. The way kids are taught calculus in high school ignores everything Newton did because it's not the most efficient way to teach kids how to solve AP problems. But without going back and learning about the questions that Newton was trying to answer, you don't actually understand how calculus works even if you can do it by rote. So at best kids learn it for the test and then forget it because they don't actually understand how it works, and more likely they never really gain any ability to begin with.
Sanger's essay is in praise of school and formal education, but in fact what's taught in school is more often than not just a showy pretense of false economy. It's only when you leave the classroom and have time to really engage with the classics and other substantive works on your own that you can actually start to understand how the world actually works. Don't get me wrong, some form of formal education would be the best way to learn if it actually delivered what people said it did, but it doesn't. This whole essay is intellectually dishonest because high schools and colleges don't even deliver anything remotely close to what Sanger is pretending, at least not for the vast majority of people who go through them. But then again, Sanger has been pretty much full of shit for the better part of the decade. If you actually go through and read his original writing on this topic, it's clear that what he really wants isn't a more intellectual culture, but rather a free pass on being able to make up facts without citing any sources because he has a Ph.D.: http://www.kuro5hin.org/story/2004/12/30/142458/25
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.