I consider "gamification" to be the application of game design in contexts that aren't inherently games. However, those same tactics that are effective when "gamifying" a product or community are also successful when directly building a game. This is because gamification is game design. Broaden the topic to game design and we'll see much wider engagement from the larger community.
Limited Overlap: Game Development The Game Development site is primarily focused on the development (or engineering) of games, not their design. This is clear from the top 10 open questions:
- Is there an optimum set of colors for 10 players?
- Fixed time step vs Variable time step
- How can I store game metadata in a .png file?
- How do you prevent inflation in a virtual economy?
- How was collision detection handled in The Legend of Zelda: A Link to the Past?
- Why are MVC & TDD not employed more in game architecture?
- STL for games, yea or nay?
- Has piracy ever resulted in a developer getting shut down?
- Role of systems in entity systems architecture
- What makes a computer opponent feel alive?
Only #4 is an overlap. There is some overlap between many stackexchange sites, but Game Design and Game Development are really separate roles that contribute to the product released to the market. These roles of course interact with each other and that will represent an overlap between the sites, but the audiences are distinct and will best be served by dedicated sites.