I've noticed that particularly in web development there's a lot of dogmatism and feel that a lot of the "best practices" (I personally hate that phrase...) being thrown around are just a way to make web developers feel like they're qualified and superior just because they can say "I follow the rules, you don't!" It's about making websites, not some sort of pseudo-religion. Do what you think is the best way to present your content, don't be a mindless follower.
After all, who goes around viewing the source of webpages they visit (unless something is terribly broken and you want to find out why)? If I can see the content I couldn't care less.
This is from the perspective of someone who has done a lot of "web development" with nothing more than a text editor and a browser (or several)... I've used w3schools as well as the official HTML specs; I don't care what the latest fads are and don't even want to expend the effort to, I just do what works to show the content I want to show to my visitors and that's it.