"Blend Text/RGB Colors Using Gamma" should be a document or layer setting instead of a global setting. The user should have the ability to set the default option. There could still be a global setting for documents that don't have specified gamma blending settings.
Here's a simple scenario:
A designer makes a graphic in Photoshop CS5. The Star shape and text layers are each set to black with layer fill set to 45%. All Photoshop color settings are at default. The file is sent to a user with CS6 or the designer upgrades to CS6. The Shape and Text layers no longer look the same. Mass confusion.