Just to let you know, I don't think your survey is well thought-out.
Example:

Built in editor
The game engine has a built in editor in which you can build levels visually.[/quote]
Scale: from "trivial" to "crucial".
No idea what "trivial" is supposed to mean in this context (i take for granted it means "irrelevant").

But the really scary thing is that you name "internal editor" over and over.
There has been a time in which having your own editor was considered cool.
Those times are long gone in my opinion.
Personally, I now think providing dedicated level editors are a sign of bad planning.

All the popular commercial game engines have "internal editors" while the smaller, not so popular but yet very functional game engines might not have one

Sorry but this is a gross over-approximation. The amount of functionality provided by - say - UnrealED is huge, yet most content is authored outside UnrealED itself.
Do your research, Collada is here exactly to solve the communication problem between different programs.

If a game engine - especially a 3D one - is supposed to be used for a project with multiple people, how is having a visual editor of a sort NOT necessary? Sure, you can have everything built in 3DSM or Maya and just import the scene, but it'd be impossible to directly test game logic and the graphics within the game engine.

I don't understand what are you talking about. Even with an "internal" editor, such as UnrealED, which I consider the slickest around you don't test the logic directly. You run a compile pass and load it up. Those compiles can take hours... or might take a blink of an eye.

If a game engine - especially a 3D one - is supposed to be used for a project with multiple people, how is having a visual editor of a sort NOT necessary? Sure, you can have everything built in 3DSM or Maya and just import the scene, but it'd be impossible to directly test game logic and the graphics within the game engine.

I've worked on quite a few commercial games that worked that way. There's a lot of proprietary engines used by big companies besides Unreal/etc -- most companies have their own engine that you've never heard of, and will probably never see the toolchain for.
The last console game I worked on, Maya was used as the "level editor". In-game, you could write test/debugging tools in Lua so that you've got extra controls in-game -- e.g. mid-game I could pause the action and enable an IK GUI overlay that shows a whole bunch of rotation axis on the screen, or enable a menu for overriding AI actions, etc... We didn't have an "editor" for our engine at all, just a decent debugging layer built into the game, and a toolchain connected to our regular (non-engine-specific) art/programming tools.

Every engine worth it's salt support real-time reloading of game data and script-code these days anyway, so if you want to iterate on a texture, or some game logic, you just edit it in your art/programming tools, and the game updates on the fly while you're playing.