And honestly if it was the other way around and the TiVo platform was being introduced now I doubt it would be any different. At some point you have to choose which bits of backwards compatibility you don't keep.
Radio as tunable channels predates TiVo on Virgin Media (and recordable boxes) as they were on the previous Digital TV boxes which again replicated the separate FM feeds that some cable franchises had in the analogue days.
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I work for Virgin Media - but all opinions posted here are my own