I'd hazard a guess that one of the reasons its not a feature in the UK is import duty.
PVRs attract a high rate of duty.
Sky got round this years ago with Sky+ by convincing the UK courts that PVR functionality was a subscription service and not a feature and one of the reasons they used to charge extra for it, before the costs were absorbed into the packages.
Manufacturer's of other end user PVRs (Freesat, Freeview etc) get round it by manufacturing in the far east and then doing 'final assembly' (they fit the HDDs) in eastern Europe usually.
Generic/FTA PVRs don't have HDDs fitted, and you have to supply and fit your own, or pay the reseller a premium to supply and fit for you. For the same reason
So probably why there are plenty of TVs on the market in the UK with USB that allow PVR functionality, but none with it intergrated.