Well, you seem to be mixing a couple things together here.
1. If you bet and no one calls, you don't have to show anything (which you already know).
2. You can just show one card.
3. Not just anyone can ask to see your cards, basic poker rules indicate that it must be someone that was contesting the pot. This is not to be taken lightly as the normal reason for this is to stop collusion not to allow players to collect information on an opponent.
4. Anyone abusing the right in #3 can have it taken away by the cardroom mgr or tourney director.
5. Anyone actually pulling #3 better damn well have a good reason for it as most people won't like it.
6. Any deviation by the morons at WPT are likely because they are huge control freaks and have written rules that don't apply in the real world but can be enforced under the umbrella of their stupidity.