Most Brits probably never use the 115V side for anything. I think the biggest use is likely to be in those hotels which cater to a large international clientele.
On the RCD angle, yes, the point of the xfmr is that it removes the ground reference from the shaver supply.
If you put an RCD on the primary side, it would have no effect on the output even if one pole of the latter were to be grunded.
If you put an RCD in the floating secondary side, it would still be of no use because touching one side of the supply while in contact with earthed metalwoirk would not result in any substantial flow of current (only a little leakage due to capacitive coupling).
