But it still reflects a lack of knowledge about relational theory that is a bit unsettling to me.
I think the key quote is this:
I had thought that the use of the ON clause versus the WHERE clause was mere eye-candy, and that all conditions were treated identically no matter where they were placed in the query.
Well, if you only know Oracle and SQL, that's pretty much what I'd expect. But you _should_ know more than that, shouldn't you?
SQL (at least the version used by Oracle) obscures the difference between join and non-join conditions, but you should have known that already.
And yes, learning is good, no matter what your position, but I'd still expect someone who writes and edits books about databases to know better.