I'm almost certain that the TV licensing people don't need your phone number or date of birth. I've bought 3 TV's in the past couple of years and never been asked for either. So they might have been hoping people would think that, and indeed some of the information might have been, but it does sound like they were throwing in a little extra information "for good measure".
Going back to this- and this is possibly worrying- When I worked in retail 5 years ago, we were trained to take this information, It was only on hardware that could recieve TV. We were trained that the purpose was for tracking people who did not pay for their TV license.
We also took details of people who bought radio transcievers that were possible of listening in on, say, police frequencies.
Maplin Electronics by the way.