To target passionate enthusiasts while retaining control, they could have waved the initial $19 fee to anyone who signs up only during GDC week. IIRC Unity did

To target passionate enthusiasts while retaining control, they could have waved the initial $19 fee to anyone who signs up only during GDC week. IIRC Unity did something similar a couple of years ago with their 3.5 non-Pro mobile plugins, shortly before releasing Unity 4, and the experiment eventually convinced them to provide free non-Pro licenses across the board (consoles excluded of course).