Licensing is *all* semantics! Apple only sells upgrade licenses to its software, however, for anyone still confused.
Apple doesn't have different licensing levels, so the term Software License Agreement doesn't require any further clarification, but I assure everyone that it is not a "full" license in the legal sense. Trying to draw distinctions from Windows regarding activation and serial numbers is irrelevant--those are simply implementations; there is no requirement that a full retail license have serial numbers or dongles or activation or registration or what have you.
The only actual distinction between what is colloquially called a "full retail license" (better known in the practice as a "standalone" license) and an "upgrade/update" license is that full retail licenses must be compatible with "bare" systems (which is not the same thing as "blank"). As Apple does not sell bare hardware at all, there is no full license available to the software. If Apple offered a "full" license, it would be more difficult, legally, to restrict the OS to Macs (but still possible).
Variations on a theme, as it were. The prerequisite to the stacked license is different, but not the requirement itself. It has shipped those discs as "updates" and the only distinction is that rather than requiring an initial license of OS X, it requires an initial installation.