Could it be perhaps those new tyres you had put on your fronts that have a far better rolling resistance than some of the obsolete OEM crap that VW uses?
I'm still on the same tyres all round - PS3's.
I totally agree that weather does play a part, but we are not exactly tropical at the moment and this winter has been fairly mild.
Lots of other things can play a part - do you live in a hilly/flat area? Driving style - is the driver reading traffic well enough ahead to coast to a slower speed, rather than braking and accerating etc. So I agree with you that it might not just be the engine for me or countless others when we see changes in our mpg.
All I was trying report on was my findings and whilst weather may be playing a part, nothing else has changed, so I have to assume that the engine loosening up is a big factor in the improved mpg.