Broadly, I think that you are right. If you are going "group A" from scratch and can get a JAR PPL, that has to be the preferred route and the cost penalty is small since you basically still have to learn the same stuff in the same aeroplane.
Reasons to go for NPPL? - well obviously medical, but also if you are an existing NPPL(M)/(SLMG) holder with any significant hours, then the SSEA conversion is much cheaper than the JAR/SEP course if you don't specifically want night/IMC capability.
If you hit a medical issue later, moving from JAR-FCL PPL(SEP) to NPPL(SSEA) is pretty trivial. Similarly, if you plan to fly SSEA/SEP and something else, then SSEA/SEP is usually the easiest baseline, then add differences training to the other aircraft classes.
G