Seriously? I always just change over without touching any readers at
all, just like changing between Tube lines, and it works fine.

I specifically queried it because the Oyster blurb does talk about touching
out and in when changing from one mode of transport to another and the tube
and National Rail are most definitely two different modes. In that case it
does make sense to have an exit and an entry and use both validators.

To my mind your approach makes more sense though. One entry and one exit
seems right to me.