I really think they should send out emails letting you know about seat changes! And Uncle T- keep an eye on your September 2012 flight too!
Whilst it is bad news, BA are doing something that makes sense for them. The 70J 744's normally used on the 217/216 service are probably better used elsewhere, I remember you saying a while ago that you have been on flights that have been very lightly loaded on this route! Also, remember BA always say that you may be moved for operational reasons and (in your case) your 63AB are not 100% guaranteed! I would secure 15EF, these are good seats and whilst no 63AB, they are not 37DE either...
Don't change to Beardy's airline, the reasons for that are that you can't UUA quite like you do, no seat selection or lounge on the JER-LGW-JER sectors which will be in ET unless you want to pay silly money for CE as you would lose Silver and also no through ticket. If you were not from JER, changing airline would be easy but travelling on a through ticket when living in JER makes complete sense.