Leigh when you say flexibility is neurological are you saying anyone can do the splits if their brain works the right way and some can't ever? Or did I get that totally off base?
Your muscles are controlled by your CNS. Having the right neural set up is why some guys are stronger p4p than others. The CNS controls the contraction of the muscles and if you can coordinate them with more efficiency, you move more weight. Your strength will still be limited ultimately by the size of your muscles. Your genetics will limit you but you can make the most of your genetics through training, diet etc.
Flexibility is very similar. A coordination of muscle tension (or lack thereof). You are still limited by your genetics but practising your flexibility will make a big difference. Static stretching does not help much beyond beginner gains though. You need to practise the movements you wish to be flexible at, eg if you want flexibility for high kicks, you need practise high kicks. If you want a good rubber guard, practise rubber guard.
Neurological adaptions are pretty specific, which is why wrestlers can be so much stronger on the mat than in the weight room and why some guys can head kick without being able to do the splits.