just some interesting background about thunderBolt:
Originally, it was going to be a fiber-optic ONLY system. But while they were still evaluating it the lab, prices for fiber optic were not coming down fast enough, and fiddling with the interface (including shortening cable lengths) showed that its COULD be supported over copper.
So copper ThunderBolt is what got released, and fiber-optic versions of Thunderbolt are available, but have not yet descended to 'consumer' level prices.
A side note is that Fiber-optic Ethernet-equivalent cables HAVE gone way down in price, putting them within consumer reach. At this writing you still use a double fiber for ordinary uses, one for transmit data and one for receive data.