The reason they didn't use Light up until now is due to price. The silicon controllers for a light-speed interconnect were very costly but now that Intel has designed some new controllers based on their 32nm fabrication technology it has brought the costs and performance in to an acceptable realm for commercial application.
Also it is inevitable that lightpeak will take over USB 3.0 for a few reasons.
1. It is going to use the same physical connector as USB and be electrically compatible with USB 1.0, 2.0 and 3.0
2. It can supply as much power as USB 3.0 to connected devices
3. It can pump multiple protocols through the 1 cable including USB, Firewire, Ethernet, DVI, Display Port, HDMI (With Sound)
Light Peak has been designed to be the last connector you ever need. Able to fill the needs of all other cables and in most cases at greater cable lengths while remaining physically compatible with the most popular cable to date which is USB.