It shows that LHR is a strong selling point for BA. Much more than a free drink and nibbles. On the same day Ryanair offer a return to STN for £60, easyJet to LGW for £100ish. People seem to be prepared to pay a massive premium for LHR. It would be cheaper to fly to another airport even with a longer taxi ride, but LHR is a massive pull. A freebie would be nice but the fact is they don't need to.