This has been an interesting question for some time.
If you have an open circuit to the reg you can see the pressure on the beer.
With a non-return/check valve, you only see the pressure in the reg.
Both have their advantages and disadvantages, for several years we sold the CIG Bevireg, that comes with a NRV (non return valve) built in, now I sell the Micromatic, over the last year we have sold nearly 100 Micromatic regs, 1 person has managed to get it wet.
None of them have a NRV, customers all get told how to use the reg properly and the evidence would suggest that they are listening.
Personally I think the advantages of knowing the true system pressure outweigh the minor risk.
Just be careful.
Hope you all have a very well wet 07.
MHB