That's because Face Time only works over Wi-Fi, which tends to be more stable for video connections than 3G data networks.
Still, the option to make video calls, even of slightly poorer quality, wouldn't hurt.
When this action happens in each of the other video chat applications, the video feed simply freezes for a split second before it reappears jarringly with different video.
Apple's solution to that admittedly small glitch adds a bit of cool to Face Time.
The next step in the process is to set up an Apple ID (if one hasn't been set up already).