I am no fan of Limp Bizkit, but from what I understand, the accusation that they 'stole' material from their fans is skewing the information a bit. Guitarists were allowed to audition for the band as part of a publicity stunt, and signed forms that spelled out what would happen. The main reason they were asked to sign away those rights was to allow Limp Bizkit to make a video of the search. I sincerely doubt that the 60 seconds each one of the thousands of guitarists had is going to somehow create some sort of satori in the band, based on a poor rendition done in substandard settings with less than ideal equipment. Most of the dissatisfaction from the LB situation appears to be from people disgruntled that they didn't get what they consider a fair chance, and turning that anger on the band.
As for the WOTC situation, similar protections are needed for this competition. Furthermore, as has been mentioned, the single page summary isn't going to provide a masterful amount of material. If WOTC merely wanted to steal ideas, they'd just cruise the story hour threads, not hold a competition that makes them a target for such accusations. The one-page summary is as much a test of the writer as the setting. How well the writer conveys his ideas and hints at how well he can expand upon them is crucial. Given the limited parameters of the summary format, how many individual ideas do you actually think they've seen? I'd wager far fewer than you might think.
Now, if you want to spend time worrying about how people might be mistreating you, that's certainly a way to spend your time. I just have no intention of joining you.