As far as I am aware, WotC has all kinds of internal policies regarding fan-made material that are far more fair to fan works than people tend to give them credit for. For example, I am fairly certain that various Magic: The Gathering designers are forbidden from looking at various parts of the Magic forums where people put up their own content, and that even if you send an idea to a D&D designer in the mail he will be forbidden from reading it due to company policy. The WotC designers and developers are being paid to create their own ideas, and I think even their own management would frown on them stealing ideas from other people.
Honestly, unless someone can make a solid claim about WotC taking someone's idea and using it in one of their products, then I think this is all just paranoia. I know I have seen tons of great original material on those boards that has not been stolen, so there is plenty of reason to not be afraid.
Also, what mudbunny said is quite correct. Honestly, for something that I wouldn't want to publish, what is said in the terms of service doesn't matter in the slightest. For stuff that I would want to publish, I wouldn't post anywhere, certainly not a forum, and without a doubt that includes ENWorld just as much as the WotC boards. Actually, the prevalence of third party publishers on these boards probably makes them an even worse place than the WotC boards to post something you think is publishable.