With sky doing a major hardware upgrade (replacing all the MPEG2 only decoders with modern ones so they can shut of the duplicate MPEG2/MPEG4 broadcast, freeing up bandwidth), a bit of a dip in (partially lower margin) subscribers is probably not too much of a bad thing.
I suspect they waited untill after the RWC for their change over to reduce the number of new decoders they have to pay for.