LHR-OSL on some dates in June, for example seems to have exactly the same fares today as it did when I booked a flight there on about 6 March. Certainly, this doesn't look like the mass revenue grab from a captive customer base that "BA enhances short haul fares" could lead one to think.
However, if the gap between HBO and fares with a bag continues to widen, those of us who have to check a bag because of what we carry will not buy HBO, we will buy elsewhere. We are in a minority, so BA won't care.