Your other idea is more lamebrained than membraned. That won't hurt voice or speaker quality to place a waterproof membrane over the speaker ports, microphone and earpiece, now will it? Seriously? The people who fret over the risk of dropping their phone into the drink can go get one of those aftermarket solutions (I think they run over $100), but OEMs don't have time for such nonsense.
It’s fun sometimes talking to someone with absolutely no imagination but I find it quickly get boring. Gotta go, bye.