CRC used to be order one day, receive the next even if you ordered quite late in the afternoon. Wiggle were pretty much the same, even if you went for free delivery.
Now though they definitely seem to be slower & I don't think it's due to the postage, but the order processing. It used to be the case that you'd get the order confirmation very shortly after actually ordering, but now the order sits at processing for a couple of days before anything happens.
The problem (as I see it) with Wiggle & CRC is that it always did used to be next day, even if that wasn't what the postage information necessarily said. People get used to a particular service, and then when the service 'deteriorates' to something approaching what is actually still a pretty good service in terms of order turnaround, it is seen a poor service because it 'never used to be like that'.