Hero member just means they've posted over 450 times (on average) over 450 days, or made 14 posts each 2 weeks. This means you can add more content to your signature, and it makes your account worth more on this forum. This typically also means a user has more experience with this board, and has interacted enough with everyone else to know what their doing.

Mike Hearn is not a very rich or important figure when it comes to Bitcoin, his announcement was merely timed with the cryptsy collapse announcement, and they merely compounded on top of each other to form an issue. Mike had no individual effect, he was just waiting to make himself feel relevant.