Unlike a viewer on YouTube, when someone hands over their email address, you have the ability to follow-up with them, to continue building the relationship and

Unlike a viewer on YouTube, when someone hands over their email address, you have the ability to follow-up with them, to continue building the relationship and (when the time is right) ask for the sale. It's also a lot of validation that the core concept he communicated is worth pursuing. If he put up a landing page, promoted it, and got no email addresses, that would be a signal in the other direction. 1,100 email addresses from people to volunteered them in response to your idea is nothing to shake a stick at, especially in such a short period of time.