I have no AIW hardware at hand to look at things, I'm just describing the situation with TV-in hardware.
The video encoder chip can do all standards, and that's probably why all video-input software offers you a switch - and that'll work perfectly fine for your VIDEO inputs (if any).
Now, for TV signal there's a tuner and HF demodulator in front of said video encoder chip. Discrete analog-component tuners hardly ever are multi-standard, while the recent silicon chip tuners mostly are.
Feeding a PAL input into an NTSC tuner will get you loss of color, possibly no stereo audio, and if the tuner is really stupid, also no vertical sync.
Also please note that the only mention of NTSC and PAL in the manual GStanfor linked is for video /output/, not input. Just like the video-in chips, the video-out circuits in graphics chips are multi-standard, and there's HF modulator attached to them either.