In case you wanted an answer to the question, Matt Burns gives it up in CrunchGear:
“Light Peak”, as it was called up until it was rebranded “Thunderbolt” today, promises a new world of screaming-fast data transfers. The claims are spectacular: 10 gigabit per second transfers (both upload and download!), dual protocol support, and power over the cable. Light Peak… excuse me, Thunderbolt, is truly the interconnect of the future.
And, what it means:
This sort of explains why there’s only a single Thunderbolt port on the new MBPs. Nearly anything can be run from this single port: DisplayPort connections (big ol’ high-res monitors), data transfers (big ol’ high-speed storage drives) and, with the right adapter, DVI, HDMI, VGA, FireWire, eSATA, and Gigabit Ethernet will work with existing PCI Express drivers already supported at the OS layer.
In other words, very fast connectivity, many different devices, only one port necessary.