Sky Camera System is popular and valuable to devs

1. Control Schemes
2. Hardware
3. Development

Sky Camera has the ability to use many different control schemes.
Movement based: See Legend of Zelda. You can only move in four to eight directions.
Aim(mouse) based: See Diabo II. You move your mouse around and click to move in that direction.
Combo move/aim based: See Alien Swarm. The ability to move like Legend of Zelda, but aim like Diabo.

FPS'er evolved based: See Elements of War.
Movie: ( http://www.moddb.com/mods/elements-of-war/videos/elements-of-war-sky-camera-system )
Screenshot of how it should really look: ( http://www.moddb.com/mods/elements-of-war/downloads/elements-of-war-ut2004 ) 

It's a FPS'er from the sky. You may or may not allow camera pitch and or zooming. FPS'er based is mainly for 3D games. 2D games are possible, however. I think if you want 2D, you'd have to figure out how to change the textures based on where you're at and looking from...

RTS based: The camera isn't always stuck to the player. You can move it wherever in the level or only so far from the char.

TPS'er evolved based: See World of WarCraft. It's less aim based and you can easily get away with higher/lower terrain and camera pitch.

Conclusion:
This is great for new players as they can easily grasp moving and aiming. More advanced players can have more control and do interesting things. I firmly believe the FPS'er evolved based sky camera is underserved. Most developers are sticking with the more n00b friendly movement or aim based sky camera. While this is fine now, I easily see players drawn to the game that will use the FPS'er based control. This is simply because FPS'ers are easily one of the most popular genres atm and heavily skill based.

Hardware:
You can have less client and server specs using a sky camera. Unlike a FPS'er where you have to see deep in the background, a sky camera only allows so much on screen at once. Without the deep background, you can add very lush graphics and get away with it. The added bonus to the client is also included to the server, as it won't need to send/recieve as much network packets or whatever. Developers won't need super complicated a.i., as you'll only be able to see so far away.
Porting: Because less specs are needed, it's easier to port.

Development:
Sky camera is much easier to make levels for than FPS'ers. You can also easily copy/paste a ton of your content. Your tools might even be really simple to use, which is a major bonus to modders(Game modifications). If you've already got a 3D engine made, such as a FPS'er, it's easy to slap a third person/sky camera system over it. Less time spent making a.i. The camera view distance is normally 400-1024 (anything past that is really pushing it), meaning players aren't up close and personal with your char models.

// Curtis Turner - IceIYIaN
// Creator of Elements of War!
// http://www.ElementsofWar.net/ 
// http://www.ModDB.com/Mods/Elements-of-War