Remeber- they still do release F and W redemptions for most flights, but you have to think of this in terms of the SMALLEST cabin size of any one aircraft in the fleet. The 789 only has 8 F seats. They could hardly allow a certain amound to go to award space if they were certain they could sell that very small cabin.

On the matter of W- don't forget that while most BA aircraft have 5+ rows of WT+, some beach fleet 772s at LGW have only 3 rows of WT+ seats (24 seats)- making this cabin quite small.

Therefore, I honestly think BA not guaranteeing seats in these cabins is fair. These are very small cabins compared to Y and J- they are niche. But, as I said earlier, BA do release seats on most of these flights in any case. (In fact for me, I tend to see WT+ avalibility over WT most of the time for IAH).