Well if someone walks in front of your TV while you're playing your Gamecube then your game is interrupted as it is.
Also the 30 degrees of pointing sensitivity means nothing more than you'll have a hard time playing while standing 1 foot in front of your TV. ie the closer you are to the TV the greater the angle (from your pointer or remote) to either edge of the TV screen will be. ie it will exceed 30 degrees. That's all. Nothing to see here. Move on.
IF this 30 degree number is true and you want to get an idea of how far you have to be far your TV to play then here's the calculation.
Measure width of TV. Tan 30 degrees ( or ~.577) = Width TV/2/X with X equaling distance you must be from the TV.
For the 23" standard TV in my office I would have to be at least 16.9 inches away from the TV.
If you have a 50" widescreen TV you have to stand at least a shade over 3 ft away from the TV.
edit: The above is done with the assumption that 30 degrees means in either direction of center. IF it's total then the numbers are doubled and then some.