jdechko,
Just because all Macs come with an OS, does not mean that Apple has been selling "upgrades" all along. Up to this point, each version of Mac OS X purchased is a full licensed version that have not required any particular previous version. For example, Leopard is not an upgrade. Your conclusion is not logical.
S-
At this point, you're just splitting hairs and in a logical fugue yourself. You're giving the conditions for a scenario that doesn't exist because each time someone gives you a similar example, you split the hair further. Precedence exists for Apple to do exactly what you're describing as illogical.
The point being that you don't know with certainty what the conditions will be until Apple says and Apple hasn't said so yet.