I have just gone through a bit of a drama with Rapha regarding the sizing of their jerseys.
First of all, I have to say they have been more than fair, and exchanged my jersey that was bought for me for Christmas. I have only just realised it didn't fit correctly, as it hadn't been jersey weather until recently. It had been worn and washed (I was up front about that to them), so I can't complain about the service.
The jersey was marked as a large, and as I have 4 other Rapha jerseys in large, I assumed it would be the same. After a couple of wears I felt it was just too big, so measured it from armpit to armpit and compared this with the same measurement of my other jerseys. It turned out to be 6cm bigger around.
After a lot of to-ing and fro-ing with Rapha it turns out that the current medium is the same size as all my previous larges. They sent me a new medium and all is okay.
This seems to me to be all part of the shift of focus of Rapha to the American market. All the Rapha rides are now in the USA, and I think the sizing thing is part of a shift toward the larger sizes the Americans use to make them feel normal size (like the size zero of the USA is equivelant to size six in the UK).
I know the US is a big market, but I hope they don't continue to move away from the UK.