That is of course to implicitly accept that the criticism is in fact valid. It is rebutted later on the page, below the letter, with an argument that, in a mod

That is of course to implicitly accept that the criticism is in fact valid. It is rebutted later on the page, below the letter, with an argument that, in a modern form, would be something akin to You would reasonably expect a visiting professor teaching Web design to complain about the lack of a WWW browser.