For any of those interested…I have just read a theory on another site which seems very interesting. I am not sure how correct it is, but it seems to make alot of sense, somehow. Its fairly similar to what a few of you have commented above, but a little clearer.
Basically, the Red Bull, as we all know, has a more pronounced rake than the other cars. That is to say, the angle of the floor is steeper than the competitor’s cars. This means that the reference plane, (imaginary by the time it is under the nose) would actually be under the ground when it was level with the front wing. So although the front wing is flexing (and I know that is an entirely separate legal issue) it is still above the reference plane at all times.
Having said that, as most of us have agreed here the flexing of any bodywork is not permitted, and so that is a separate question to the one of the reference plane. But interesting nonetheless.