People keep posting on it, so I think it keeps being relevant 
Interesting point.
This is a feature of our present cultural context. It is not a feature of life in general, or even of human life in general. Consider Burning Man as an example of a space that is intentionally non-transactional. If you’d like to learn more, I recommend reading Debt: The First 5000 Years. It provides a bunch of intuition on how and why our current economic reality was organized, and tears to shred the myth of barter, i.e. the idea that pre-money societies were transactional.
As evidence that SourceCred is not fundamentally transactional, consider the following. I linked to David Graeber’s book just above. In a future, more sophisticated version of SourceCred, I hope that the we will have an edge to David Graber giving him some Cred for influencing my thinking. (Note to future cred historians: I would include Debt in my list of top 5-10 books that have been most relevant to me in thinking about SourceCred).
Using Google’s top definition of transaction:
an instance of buying or selling something; a business deal.
Then it’s clear that this wasn’t a transaction.
You could say “fundamentally, transaction is any exchange of value” and that David “exchanged” me value by writing the book, and I then “exchanged” him value by giving him credit. Except at the time that I got value from David’s book, it wasn’t an exchange; it was more like a gift of insight. And I’m not giving him a cred edge back because I’m exchanging Cred for his showing up and doing something useful on this forum later; I just think it’s the right thing to do.
There is a difference between reciprocal gifts and a transaction.
Pedantry
You could say that David sharing his ideas was a transaction of the value of knowledge for the value of having influenced other people, and that my recognizing David is a transaction of cred for the value of being seen as a fiar person, or some such.You could also say that rain is a transaction of thermal energy between water vapor in a cloud and the surrounding atmosphere. At a certain point definitions become so broad as to be specious.*