DVDs have different regions. It's an intellectual property rights issue rather than a screen resolution issue.
Edit: If you google your particular DVD player, you may find that there is a cheat code that you can use to play DVDs from a different region. For example, on my old Magnavox DVD player, if you push the number 1 on the remote four times, it will play DVDs from all regions. Or so I've been told. I've never had a need to try it.