that your neighbour is on 40mbit/s down 10mbit/s up
Which, in reality, is likely to be pure marketing drivel because of contention, packet-shaping and rate-limiting. Just like in today's ADSL world. The residential market will always be a volume market where the preference is to fight on price rather than quality.
FTTx becomes (shock, horror) successful
I'm not saying it will never become successful. Just saying there are many reasons to be cautious about BT 21CN, and thus there are many reasons why signing a 12 month contract on existing technology in order to get a good deal is not exactly stupid either, 12 months isn't exactly very long either.
And by the way, coming back to ....
BT have sunk a LOT of cash into this rollout
I forgot to mention the obvious that if they did not sink "a LOT" of cash into this rollout, then BT would likely be just commiting corporate suicide as they wouldn't have a competitive network going forward. So there wasn't exactly a great amount of choice in the matter.