Those who say that the CAA always prosecute in cases of fuel starvation are a little out of date. Earlier this year I attended a CAA safety evening at Fairoaks in which we were given a talk by the CAA's current head of enforcement. He mentioned that his predecessor had a particular penchant for prosecuting fuel starvation cases, but made it clear that he personally did not agree with that emphasis.
The current view seems more enlightened. The role of enforcement in this area is to improve safety by detering pilots from doing dumb, dangerous or reckless things. In selecting cases to prosecute, it makes sense to pick those where the deterent effect is significant when the decision to commit the reckless act is made.
I don't know about anyone else but my motivation goes more along the lines of "I'd better load enough fuel or I'll crash" rather than "I'd better load enough fuel or I'll be prosecuted".