Like you said, wet figures reduce the margin for the go case. You will have a lower V1 to account for a longer stop but on a dry runway you would normally stop up to a higher speed using dry numbers.
Have an engine fire at a wet V1 on a dry runway and you go flying on fire with reduced margins, if you were using the correct figures for a dry runway you would have plenty of time to stop.
Seems a bit stupid to me.