This site could be so much more if there were more game design questions asked. I feel when someone says game development they immediately think game programmer.
When developing a game you have to first come up with an idea, implement the idea with some type of prototype( could be paper ), decide if it's worth pursuing, implement a simple digital version, playtest, make changes, test, test, test, add new rules to balance, etc...
All of this is the development of the game. If this site is just going to be about game programming, can we please make a corresponding game design stack exchange because that's the hard part not the programming.