Jaya
As I said before, I have no problem handing in a passport to hotels , - this is the law but it IS HOW it is done I'd complain about. Why should I place trust in people I don't know?
Nothing in life is foolproof but passports could still be handed onto someone dodgy if a guide handed them in!
There have been horror stories on trip advisor of how a tour guide collected passports in Vietnam at Halong and the following day hers went missing and it was never found. There was someone's blog on Cambodia where a passports were robbed, attempts to extort money for their return and the hotel were in on it.
And let's face it, if a hotel or guide lose it they are not going to take responsibility or pay for a new one or expenses incurred while awaiting replacement. They will just say they gave it back to you.