NTSC is pretty much universal in the world of classical music DVDs. I suspect PAL pitch-shift issues play a part in this, but since the US and Japanese markets are significantly bigger than the European one, that's probably the major factor.
Up to a couple of years ago I worked in a classical music shop and the pitch issue was certainly very important, NTSC even being for European-only releases (though of course it makes it easier to port - or import! - from one region to another). Most classical buffs - more knowledgeable about music than technology - wouldn't buy them if they suffered from a raise in pitch, though I know there are other ways around this.
In the shop we got many complaints or at least queries from customers experiencing difficulties playing NTSC DVDs. Apart from a few who had very old TVs, they could play them but had to make some adjustment. Some poorer quality Scart leads (which many used then) wouldn't carry NTSC, or only one of the TV's Scart sockets would input NTSC. Sometimes the picture would be in black & white only.
Most problems though required some adjustment to the player. My first (Toshiba) player was factory-set to play PAL only and had to be changed to play both - a simple enough adjustment in the set-up menu but many older customers, who were used to tapes, had to be guided through it. My second player (a cheap multi-region Mico) plays everything in PAL - automatically converting NTSC discs (which can be useful!) - unless instructed otherwise every time I switch it on. Even my current Panasonic DVD hard-drive recorder cannot be permanently set to recognise NTSC discs because it of course needs to default to PAL for UK TV broadcasts. It displays an "Incompatible system setting!" warning every time I insert a NTSC disc and I have to go into the set-up menu and change to NTSC; not a problem, but if I forget to revert to PAL (very easy to just switch off after watching the NTSC disc) my TV timer recordings don't work!