Yes, but complaining about this is like complaining about the cost and inconvenience of getting vaccinated for polio: If the cure seems worse than the disease, it might be because you don't clearly remember what the disease was like.

I assure you that however clued in we all are on HN, the OP is right: The notion of the "top-secret killer idea for a website" is alive and well outside of geek culture, having captured much of the aura surrounding its much older cousin, the "brilliant idea for a movie that will make me rich in Hollywood unless it gets STOLEN". As a web-publishing consultant I had several people ask me to sign NDAs in the first half hour of the sales process, sometimes before they would even tell me why they called, because they were terribly frightened that their brilliant concept ("It's a review site. For local hobby shops. On the internet.") was going to get "stolen" by someone who would go on to reap the millions that were rightfully theirs.