We have both of these tags floating around, with game-design having more questions.
My first impression is that game-development is the practical stuff related to creating a game that's not quite "design", such as printing or patent/copyright issues. I don't know how to succinctly describe that, though.
It seems game design is very clear. The issue you have is with the confusing definition of "Development" which could include design, but may not.
It seems like simply changing the tag from game-development to something clearer like game-manufacturing would solve the issue.
I feel like game-design could be for questions about game design, regardless of whether or not one is making a game. Don't gamers love to discuss differences in mechanics between one game and another? Game-development, on the other hand, could be geared toward answering questions specifically regarding producing a game, from concept to prototype to finished product. Protoyping could then theoretically be merged into game-development, but prototyping is a very specific part of the game-development process.
