I think you'll find the majority of people with NPPLs have them because they can't get the medical certification. When you think about it, the NPPL requires, as you say, basically the same training (though there's no radio navigation), the same written exams, the same flight test, and costs the same to use when you've got it. But you can't add night or IMC privileges, or use it abroad, or convert it to use in another country. So in practice the majority of people still have the JAR PPL, unless they are old enough to make the medical issues a problem.
Tim