This discussion happens every time someone talks about rinsing first stages. I'll only say that lots of divers and lots of dive shops have collectively soaked their dust capped first stage millions of times without a problem. We've even been know to push the purge button on the seconds (gasp) as long as the first is held above the rinse water.
OTOH, there will always be people to tell you not to do it and they'll often supply pictures of corroded regs. Although somehow the outside of the regs are always a mess too which is not what you'd get from well-rinsed regs.
There's also the fact that you need to soak regs to really get rid of all the salt crystals. Rinsing is fine to clear the sand and get you to the next day's dive, but clean means a soak. Cenote/spring divers are excused here.
IMO, pressurizing the first stage only protects you from boneheaded moves likes soaking without the dust cap being in place. But if you can't concentrate enough to rinse a reg safely, adding pressurized gas to the mix changes a potential headache to a potential catastrophe.
