Hi jmone
Sorry for late reply: There are many variations of PAL, ie PAL A,B,C,D etc. many of which ,as you rightly say, were due to differing frequency allocations and bandwidths in different countries though there were some major differences in audio modulation (Ie UK PAL vs AUST PAL)
PAL M (i think that's right) wouldn't work in the UK though, as its 512 lines and is more compatible with NTSC
Mainly there are some differences in sound modulation methods which may affect playback in a DVD
But many players multi region internals do have built in conversion to remedy that and of course most European TVs have auto multi format features which compensate
SECAM isn't compatible with PAL as the video is sent out Sequentially, but again, most multi format European TV sets handle this conversion internally too, though France is now mainly PAL orientated
But I think I am getting a bit off topic
Rgds
John