JP: I think you taking the term "partner" in a literal, old-school definition.
As Wiki put it, "Alternatively, [a business partner] may be a very loose arrangement designed largely to impress customers and competitors with the size of the network the business partners belong to."
Seems it worked. Unfortunately, this is the most common usage of the term today and it has little meaning left. This makes it particularly difficult when you are actually need to describe a legal business partner.