Having said that no one wants to be the "Dropbox is just rsync " guy. Or Lily Allen turning down thousands of bitcoins (although she's successful anyway so she probably shouldn't care). If you see what I mean ... no one wants to say an idea sucks before hand, and if they do you can just say "well they said that about Dropbox".
Kidding aside, I see your point. I guess it's important to distinguish between criticism and dismissal of an idea. "Dropbox is just rsync" seems like a dismissal, not a critical look at the validity of the idea. And Lily Allen turning down bitcoin? Well honestly I'm a little with her on that one. "Oh yeah can you perform and we'll pay you with a totally legit online currency we swear." Not exactly a great sell.