On the other hand, though, I do understand the need to use the five paragraph structure (or, here in Brazil, the "three sections structure"). I, just as you, was usually pretty annoyed with these formulaic approaches to text, until I've had to re-learn all this essay writing stuff for my masters. In my college, professors and students are pretty close and debate is (really) stimulated, so I decided to throw my ramblings onto the writing professor (a very good writer, indeed). I used José Saramago (a portuguese Nobel prize winner that uses commas as periods, writes giant paragraphs, all the weird stuff) as my "strong" example, thinking it would shed the formalized structure argument to pieces and I would rise triumphantly from the talk with a Portuguese PhD specialized in text analysis. It didn't take me so long to realize why she had her PhD, and that her point of view was pretty convincing and, of course, well structured.
Kaboom! And I was illuminated. She agreed with each of my complaints. But then she proceeded to show me some texts from the beginning of the semester, comparing them with texts from the end of the semester. They were, in general, much clearer, concise, straight to the point - in one word, better. She argued that a course like that was intended to make people that do not write start to write something intelligible, comprehensible. It was not a course on creative writing. Therefore, the need for simplified rules and structures.
I do understand that this was the OP's whole point: upon reading his colleague's text, he judged it based on the rules he had learned. Then, when he talked to the other teacher, he realized that the main point of a text is to communicate something, irrespective of the number of paragraphs it has or the position of the goddamn thesis.
This rambling of mine is just to point to the other side: rules are important in some specific moments of the development of a proto-writer :)
That happens with all kinds of expressive, communicative actions we humans perform (in my opinion): photography, painting, music, poetry... All of them have some (or plenty of)rules. But these rules are not meant to be used as a "ruler" to judge if a work is good or bad, they are just a compass to guide the noobs :)
Intro, development and conclusion? Será?