Just to bring this full circle and put some closure on the issue, it took a couple weeks but the issue where the SQL Server 2012 SP2 ISO didn't actually include SP2 has now been fixed.
The new ISO is now available for download from TechNet and MSDN and really includes Service Pack 2. The original ISO was released as containing SP2, but it only provided a stock RTM version of SQL Server 2012.
For those playing along, this situation isn't new, the same thing actually happened when Microsoft released the ISO for SP1, so a double face-palm is definitely in order. We'll just have to see what happens once SP3 is made available.