3d support (monitors)

2. How exactly are the drivers such as tridef working? .. apparently they listen in on the dx calls, but with everyone rendering in different ways, how is the magic working?

Well, ultimately, at the end of their pipeline, most standard games output a frame buffer (containing color information) and a depth buffer (containing depth information). This should be enough to reconstruct the three-dimensional world as viewed from the observer - the driver just interprets this information and correctly plots the data on the 3D display. Games are free to use however many passes they see fit while rendering, as long as they give the driver the information it needs at the end (which is conveniently exposed through standard D3D resources).

Native support - The game is doing the 3d rendering and outputing the data to one of the 3d formats
Non-Native Support - Some magic happens by installing a magic driver which converts 2d game frames to one of the 3d formats

There's not really a 3d format. More common is to render the scene from the left and right eyes view and map these to the used 3d technique. When the first 3d glasses hit the market (~ a decade ago), rendering was simple enough and the drivers just offset (alternating) the view-projection matrix to go along the left/right eye view perspective. This worked only for the fixed function pipeline, but modern games use a lot of shaders and addtional informations which makes it incredible hard for the driver to guess what the image represents.

Even when reading the z/depth-buffer, it is not given that the depth-buffer represents the whole 3d scene. Overlays (gui) , particles etc. which don't write to the z-buffer would introduce artifacts. Therefore a driver solution would be more of a fake, the best 3d effect requires, that the underlying game engine supports it.