PAL DV is 4:2:0 whereas NTSC DV is 4:1:1, unless you use DVCPRO which uses 4:1:1 for both. D1 (or digital Betacam used in most TV studios etc.) uses 4:2:2 whereas the ATSC MPEG-2 standard for digital TV and HDTV uses 4:2:0.
So what does this mean? It means that NTSC DV and PAL DV handles colour (i.e. Chroma plus Luma) differently.
NTSC DV samples Chroma only once for every 4 luma samples. i.e. the horizontal chroma resolution is one quarter of the luma resolution.
The PAL system delivers a better colour result especially since it is coupled with the increase in resolution. It theory both NTSC and PAL DV end up with the same chroma bandwidth, but the different methodology gives a noticably different result.