1. Most players convert the NTSC-signal and send it as 60-Hz
PAL signal to the TV. Newer PAL-TV's can handle this "pseudo-PAL"
signal.
2. A few players output true NTSC from NTSC discs.
This requires a TV with NTSC support.
Some players allow to choose between variant 1 and
2. Both variants mean full framerate without quality loss.
3. A few players convert NTSC into a standard-PAL signal, working with
every PAL-TV. High quality conversion requires
expensive hardware to handle scaling and object motion analysis properly.
Because the quality of this conversion in DVD players is poor that's the worst
variant of the 3.
Bottom line: NTSC discs play on over 95% of DVD
installations worldwide.