What do web designers know about typography?

From Steven Coles at Typographica.org (via the open font library list):

In general, web designers aren’t typographers. Their specialty is in the realms of interface, hierarchy, and navigation. Their training does not include making decisions about what typeface to use for long passages of text.

Wouldn't take much to learn, though, would it? And is the information about the training web designers have an assertion of fact or merely a deduction?