Apple's Watch is designed to be both fashionable and functional.
Apple Revamps Thunderbolt Cable Lineup with Lower Pricing, Shorter Cable Option
Thunderbolt cables remain relatively expensive due to the electronics included inside the cables to manage the multiple protocols supported by the standard. The complexity and expense has both slowed deployment of Thunderbolt peripherals and limited support mostly to high-end devices capable of absorbing the high cost premium.
Thunderbolt cables have so far been limited to traditional copper cabling, but vendors are just beginning production on optical cables for the standard. The optical cables will allow for much longer cable lengths, but will not be able to provide power to peripherals as copper cables can.