For any body of text (or in general, any exposition of any kind), the responsibility to explain the value of the article is very much in the author's side.
Explaining the value of what you are showing should always go towards the start. Else, why would anyone bother with the rest?
Buzzard is writing for his blog audience - mostly mathematicians and not the casual visiting HN user.
Feel very grateful I was never taught this... Would have missed out on quite a lot of good bodies of text in my life I think! Pushing through any initial friction or ignorance I might have as a reader, having the patience and charity to bear with an author until you get it, was instead what I was always taught.
Giving such a blanket "responsibility" to the author at all is just such a bummer! I say let them do whatever they want, there is always more than one way to express oneself. Someone who was never taught to write a clear thesis in the first paragraph for whatever reason doesn't inherently have less to say.