David,
I did a clean install of Solaris Developer Edition 05/07 and it does have Sun Studio 12 which is a significant improvement over Sun Studio 11. I think the reason your machine has Sun Studio11 on it, is the fact that you did a live upgrade from the earlier Developer Edition. Sun Studio 12 will not install if there is another version of Sun Studio installed. I tried installing Sun Studio 12 on a stock Solaris 10 system with Sun Studio 11 already installed, and the installer for Sun Studio 12 complained that another version of Sun Studio was present and it could not continue.
Dave S.