More pixels _should_ have more data. That is, using the same bitrate for both an NTSC and PAL version is not a good idea.
As a result a PAL video can be more prone to digital compression artifacts if it is trying to get it's additional lines in the same space.
That is assuming these hypothetical PAL and NTSC discs are using the exact same amount of space.
In truth most DVDs don't utilize 100% of a disc.
I've seen PAL and NTSC versions of the same thing with the exact same file sizes leaving a quarter of the disc empty.
It's a matter of who is making it and if they're stupid.
PAL needs more bitrate for it's lines and faster framerate.