Its more of a 4:3 ratio like a standard monitor, television, or non-wide screen projection.
Approximately 40 degrees by X and 30 degrees by Y.
The formula for the distance from your writing surface is Distance = 2 times Height, if you want to know how far the Wiimote should be if centered on a standard screen.
(Correct me if I'm wrong, but that's what I got from reading for awhile.)
(Sorry if that has nothing to do with your post, in resolution terms its close to 800 x 600 ratio on a monitor. I forgot the actual resolution, it's a bit lower than that. More close to 400 x 300)