Which is a fair point. But BA have hardly shouted the policy from the rooftops. If they thought this was a positive service differentiator amongst the non-FF's then surely they would have crowed about it.

The OP and the occasional traveller get caught out because of the assumption that when travelling in a premium cabin, you will be able to seat allocate on booking. Wrong on BA, but hardly a rash assumption.

BA AFAIK is the only airline to have implemented this type of policy in the premium cabins.