[jandrese]

How is a poster supposed to go back to the 5 year old thread starting comment and change it to note that the post is out of date?

Good forum software makes it less of a sin, but that's pretty rare on the Internet. This isn't the Usenet where people's clients could be fully featured on every topic.

[BlueTemplar]

Usenet would have it worse, because there you can choose your software yourself (and pick one without that feature)?

BTW, I prefer decentralized protocols like Usenet, there are plenty of features that would be unthinkable to leave out of "modern" clients, this could be one of them !