Thanks all for the replies.

Tumbleweed - I should point out that when I make a booking in CW or FIRST -then, yes I do feel completely entitled - whether I made the booking via revenue or via MFU, OnBusiness, Miles only, GUF2, etc, etc. That, I believe is one of the main points of the loyalty schemes. By the same token, if I book an I class CW - am I less entitled than a J class CW????? Why would BA give me the GUF2 in the first place? Yes, I have paid for it - in both loyalty and not a small amount of revenue on other trips.
The only times this differs for me is with on op-up which I view as a total gift and don't expect or feel "entitled" to all the features.
Also, based the CW availability not on the seatmap, but on the seatcounter.

Sixth Freedom and Centurion - thanks for the explanations, finally makes some sense to me. The whole question was firstly to try and understand the logic and I think you both have helped me to see it.
I guess the OnBusiness works to a completely different set of rules as that is still showing availability.

Pucci - I would always treat the CSD as monarch of any flight I am on

I also wouldn't be comfortable with an extended visit in F if my son and I were still in CW. I fully agree that it probably wouldn't be fair to other passengers as well as the "why them and not me" argument.

No, if we don't get the availability opening up by then, I would consider asking Mrs. Irubi and baby to join us in CW. Or just split up for the short leg so that she can enjoy F. CW is not exactly a struggle either - there are far harder ways to fly