I had a hunch about this actually.
A couple of months ago Sky Movies 9 and 10 launched and these, though not, high definition, were being sourced from HD and will be simulcasted with the same content in HD for subscribers to Sky HD being installed now.
There was a small quality increase to the SD channels sourced from HD and it looked rather like the effect being seen on BB7 now.
BBC are planning on giving over airspace to other broadcasters like ITV and C4 on their recently launched HD service to allow them to carry out tests.
Now seeing as BB7 has had the biggest technological leap in terms of broadcast quality with widescreen, is it possible that they have modified the cameras to suit both widescreen and HD?.
They could even have the final in HD as a test and next year go fully HD.
It's just a thought.