The "more seas available" bit comes from the fact that ALL seats (except those pre-assigned for First / Club/ Fully Flexible Tickets / Golds/ Silvers / Wheelchair / UM's) will be available to you 24 hours before travel. No longer will we be holding any "buffer" seats at the airport for split families etc.
Obviously, the main objective is to put a stop, once and for all, to all the bickering and abuse we have to put up with at check in concerning seat assignments! Once the Boarding Pass has been issued, no further seat changes will be allowed. Just look at the threads by OLCI people concerning "BA Seat Shifters" - that will no longer happen except if operational circumstances dictate!
Of course, the real reason for this change is to devolve more of the airline's operational functions to computers so that staff numbers at the airports can be decreased yet further. If you observe closely, you will notice the airline is becoming more and more rigid in its enforcement of rules and less and less forgiving to customers who have made a simple mistake. Unfortunately, computers are not geared up to recognise human failings or to empathise with you!
The proof of the pudding is, though, that arrogant as British Airways might be, it was the first "heritage" carrier to pull through after 09/11 and the best performing "heritage" carrier worldwide currently - despite all the adverse publicity heaped upon it almost monthly! Our First and Club cabins are full - so full, in fact, that we are embarking on re-fitting our fleet with more Club accommodation - so Willie and the team must be doing something right!
Personally, I suspect it won't be long before other airlines follow BA's lead on this seating policy!