@sl007 @humanetech So, for example, there's the Follow activity. Everyone knows what that does, right? Wrong.
You can Follow people in a social media service. But you can't in a forum. There you could, for example, follow a topic or a subforum to get notified about new posts. It's two vastly different domains that use the exact same vocabulary in logically incompatible ways.
@grishka yes, it is the same problem as the semantic web had.
I saw @sl007 mention DELETE. If you look at Rest it is also vaguely defined, everyone doing it differently. You might only support GET and POST, have different API designs. It is not ideal at all, but it has proven to be practical.
In @activitypub et al there should be accepted ways and best-practices and standardization-as-much-as-possible. Closed vocabulary extensions.
I am less worried about big players doing things differently.