My intuition was right. The free Unity engine release was just the beginning of a new trend in the world of game engines as Epic has now released the equivalent of Unreal Engine 3 without the source code.
The world is changin', and I'm sure this trend will continue. I can even see some sort of engine-product revenue sharing model pop up with these free versions (think royalty-based sharing with products built using a free engine). My only question at this point is, "Who's next?"