But don't forget, these are celebrities who mostly just want to know about their roots, not go trawling the internet or through old documents to find the information. As has been mentioned, this is to appeal to the masses, not necessarily to genealogists. Of course there are many of us but not as many as there are of the rest of the population! The programme proved so popular that they changed it to appeal to more viewers. I must admit that if I don't know who the celebrity is or don't particularly like them, I don't watch the programme!
Interestingly, I think you get a glimpse into the personality of the subject.
On occasion, I have found the subject more appealing than I expected and have then followed him/her more closely in their career.
Or, I've quite liked someone ahead of the programme and then been less than impressed with their reactions to the discoveries.
On occasion - like, I recall, with Ruby Wax - the programme was really illuminating and shed a light on the difficulties that some people have to struggle with.
So it does have its interesting points even if you don't like/know the person being investigated - as well, of course, as the opportunity to yell at the screen at
the unwarranted assumptions,
the details on the certificates the person's missed,
the opportunities for further research not taken up by the programme,
the loose ends left irritatingly dangling,
as well as unbelievable envy at the documentation available to some lucky, lucky, lucky people.