I can understand why BA have done this. The likes of GLA, EDI, MAN, LGW, all used to have significant BA flights to many destinations, most of which are now flyBe and easyJet/Ryaniar/jet2 destinations. This perk basally encouraged passengers (formerly loyal to BA) to fly direct point2point services with other carriers. GCH's would still gain entry to BA operated lounges.

That said, I can see why GCH's don't like it being taken away. It would be a very useful benefit if you were based, or did a lot of flying, out of a city with a BA lounge, but only an LHR connection.