I agree that they should actually be called DISLOYALTY discounts but don't really see how they should be an impediment to taking up the TiVo offer. After all, surely you are just asking billing to add a one-off £149.95 charge and an extra £3 per month TiVo charge.
I have just ordered a Tivo installation online and get loyalty discounts. Phoned VirginMedia after reading this and the man assured me I will not lose my discounts (over £20!) When I told him the contents of this forum he did say he would check. I was put through to someone else who said that the only charge monthly would be £3 (already acknowledged) and my discounts would remain.