@spivonious: Yes. I think our company purchased it this way through a vendor.
Microsoft is obviously quickening their release pace. At the same time, the differences between versions is shrinking to almost the service pack level (most notably the small jump from .NET 4.5 to 4.5.1).
So, it would make sense that this be considered a "minor upgrade" and priced accordingly, or even free for purchasers of VS 2012. (Like the Win 8 -> 8.1 upgrade)