DFC you are wrong. D&D do not get people do practise on 121.5 to reduce their requirement for simulator training and any comment along those lines shows your ignorance as to what happens. Private pilots and their instructors throughout the London FIR call practise PANs on 121.5. I believe that this is because it is written in the syllabus. It's also good for the trainee to know what service is available. D&D only encourage people to train because it enables people who perhaps do not have the airmanship skills of other airspace users, to practise.
One further point. What are you trying to achieve by your statement that the UHF system has better coverage than the VHF system? Do you think that that has any effect on the way that the guys in D&D go about their task? Because if that is the case then I suggest you might want to consider a retraction. Otherwise, please simply explain.