Midland02 sums things up quite well.
The problem Virgin and the fare paying public have, is that if BA get too strong, they could eventually have a long term goal of pushing Virgin out of LHR, regardless of how good their product is, by purposely offering fares on the Virgin route structure at a loss. Eventually having a total monopoly on short and long haul out of LHR and, therefore, charging what they like.
As it is with BMI probably going BAs way (regardless of what Ridgeway says), the business traveller will have no choice when landing into LHR other than fly with BA to regional airports. The only other option would be get the train to Gatwick etc and fly with the low cost carriers which ain't going to happen.