I agree with you that it is not a very technical question which is why I didn't post it here originally.  However after so many people eyeballing it but nobody answering it, I moved it here in desperation.

I did do a search but I didn't pick up anything that answered it, this small clue was well picked up by you.

It seems the conclusion is that coinbase.com took their name from this terminology included in the bitcoin client.

I am still interested in a reference where Satoshi or an early developer actually introduces and defines the term 'coinbase'. ie the original reference as to why it is called what it is.