Hardware.
It's something you can touch, it has different architecture, it's carved from the rock of the real world. It's not an abstraction. It's there.
Arguments that separate game developers, gamers and the genre's all seem to float on this vacuous liquid called "Marketroid Hype". They are artificial and intangible. They are founded on biased abstractions. They aren't cut out of the stone of the earth.
So here's a better list, for electronic games. I exclude non-electronic mediums for brevity. A proper diagram of what kinds of electronic game developers are identified here, and also a simpler Manalysis, with leaner wording, not a thing that can be generated from Web 2.0 hyper-babble.
Also, keep in mind that these are borders, not walls. Just because you use one paradigm, doesn't mean you are automagically denied to use another, or utilize a fusion of two paradigms. It's more inclusive, and doesn't share the Imperialist attitudes of certain "game market analysts".
0. Classical Machines
PC's and current gen consoles like the the PS3. Arcade machines fall in this category too. Handheld devices are only different in terms of scale and viewport. These are the machines where you hook it up, sit on your ass, and game.
1. Networked Machines
Many sectors of hardware already have this capability, and almost prolific in all aspects of life. You hook it up, and you are talking to other machines. Almost everything today.
2. Sensing Machines
You plug in some interface device, you manipulate device with a spectrum of gestures, or within a range of motions. The iPad, a 2D sensing machine. The Wii, and all derivatives, a 3D sensing machine. A critical role in sensing machines; the player doesn't access the game world through a proxy, or an avatar (ala, mouse and keyboard), it doesn't "translate" the players gestures. Rather, the player IS the gesture maker.
3. The Cloud
You logon, you game, but the machine is somewhere else. OnLive. Zynga.
So there, a better list of what kind of game developers we are. None of these fake marketroid descriptors, and phony ass bullet-points.
Calling yourself a "social" developer is vacuous and empty. Calling studios "AAA" or "Indie" isn't really about game development, its more about developer politics.
Games are only constrained by the power of the machines behind them, and those constraints become the catalyst for the kinds of games we make.