I think tptacek is thinking of content with longevity, such as essays - observations of human behavior, for example, wouldn't benefit much from a date. He's damaging his argument by calling them "tutorials", which you and I associate with learning particular tools which will soon be out-of-date.
The type of content does not matter, can you think of any significant written work pre-internet that purposely obfuscates when it was written? Even an encyclopedia isn't shy about when it's written.
If you want your content to appear valuable vs less valuable, write the hell out of your content. Make it impossible to discount the content by making it stand out.
In science, researchers don't cherry pick and refer studies written in the last 5 years. They go back as far is relevant. They will refer back to hallmark papers regardless how old. Same with nonfiction books. Same with well written blog posts, because good blog authors often cite references to give the proper context. That's kind of the point of blogging, the power of linking and building upon what has already written. But making a piece of content float in some unspecified time vortex disrupts that.
What's more is that a clear date indicates that the author wrote it at a certain time. It makes it harder to distinguish people that copy content or write about similar copycat ideas from their more original authors.
For what it's worth, I'm not against the idea of situating your content in the best way possible. I think using categorization like tutorials/articles/essays is a better way of framing certain types of content. That can help the reader. Hiding the date meta is an attempt to help the author, while hampering the reader. It doesn't even add up.
The encyclopaedia usually has its date prominently displayed on the cover because it's part of the business model: Nudging people into upgrading last year's edition because it's "hopelessly out of date".
Well, pre-internet our family only ever had 1 set and they retain a very high base value even as they age, never felt a need to update to a newer set continually.
Point still stands though, are PG's essays devalued because he puts a year date on them? I don't think so.
