I can select 25fps or 30fps for either 1080p or 720p.
But, the DVD authoring software specifies 720p is PAL and 1080p is NTSC.
I'm not sure what DVD authoring software you're using, but that's not what the difference is.
720 tends to be used in broadcast, often because of bandwidth limitations.
The difference between NTSC and PAL had to do with the power supply, the standard definition broadcast standard, and the frame-rate (which is linked to the power supply of the countries they take place in). PAL is used in 50Hz countries, and so shoots at 25fps (or 50 interlaced frames, say for SD broadcast), NTSC or 60Hz countries, compatible with 30fps(29.97) (or 60/59.94 interlaced frames), as well as 24fps(23.97).
This all relates to SD, more specifically SD broadcasting. It's not such an issue with HD, and you can quite easily shoot 24fps in a 50Hz country, just that you'd need a 172 degree shutter to reduce flicker, as opposed to 180 degree. You'd only really shoot 24fps in a 50hz country if you were planning on initially releasing into a 60Hz country, such as the US. Otherwise, if you were only planning to release in your own country, there'd be no point shooting 24fps in a 50Hz country, as you'd just be creating issues for yourself, especially with audio for absolutely no gain.