I'm not sure. Two other popular online retailers here, Argos and John Lewis, do not have the same notice on their website when you select a TV and view the product page. It may be a law that they don't bother mentioning but that's just a guess.
[0] Actually anything able to receive TV, so covered video recorders etc too. Not sure how far it has been dragged into the internet age.
Insurance companies also require you to register any qualified property with the police if you get the contents of your home insured.