DLA and PIP are very different. The former is all about your disability, the latter (and new replacement for adults) is how it affects your day-to-day life.
Many with disabilities never see their GP for their disabilities, our twins for example.
You get various points that have to add up to get each part of the award. The mobility part is hammering many people, especially those who need a Blue Badge or Motabilty Car.
http://www.mybenefitsandwork.co.uk/pip/indexxx.php