Having a look at the new triple tuner Virgin Tivo box and the quadruple tuner Tivo premier elite I notice they both need cable to work. Why can these systems not work with an aerial feed and use standard Freeview?
Because they only have DVB-C (cable tuners). Freeview requires DVB-T (Terrestrial) for SD and DVB-T2 for HD. Satellite DVB-S for SD and DVB-S2 for some HD channels.
You can't buy the Virgin Tivo anyway, it always belongs to Virgin who will fix or replace it if it goes wrong.
The Tivo Premier Elite is a US box not available afaik in the UK.