As for the first flight, I think that as long as one has a SK boarding pass and do not run into a rule-obsessed person, it will work. At least I know it has for some friends who are not EBG but * Gold.
As for the rest, of course you are right. But I was was more questioning the business logic behind these decisions. I think I talk for many here who would not even had considered flying BT were it not for the benefits given to EBG and especially the miles awarded. I mean, these are precisely the reason why I do not normally fly S7 or SU when heading to these parts of the world.
Now when BT is about to launch their own FFP they will lose this competitive advantage and I will try to switch to OS and BD as much as possible when going east.