You can gain a lot of information about this from the following thread:
http://pokertdaforum.com/index.php?topic=253.15This is the rule which you refer to also:
RROP Section 13 - The Showdown:
5. Any player who has been dealt in may request to see any hand that was eligible to participate in the showdown, even if the opponent's hand or the winning hand has been mucked. However, this is a privilege that may be revoked if abused. If a player other than the pot winner asks to see a hand that has been folded, that hand is dead. If the winning player asks to see a losing player's hand, both hands are live, and the best hand wins.
I am not a fan of allowing players to see hands that have electively been mucked, many on here will tell you they do not have a problem with it, read the post above and you will see the variance in thoughts on the subject.
If someone at my tables asks to see a hand, in all probability they are not getting to see it, I will likely ask if they suspect collusion, the answer will be no, next hand please dealer ;-)
Regards
Stuart