Alan Baker
"Choice of HD Native Thunderbolt interface or PCIe card Unlike USB- or FireWire-based DAWs, which are inherently prone to latency, Pro Tools|HD Native employs either a high-speed Thunderbolt interface or PCIe core card to connect Pro Tools HD Series interfaces with your laptop or desktop computer. "

<http://www.avid.com/US/products/Pro-Tools-HD-native>

Steve de Mena
The Thunderbolt device is brand new. 1% of Pro Tools HD users probably own it.

It's also NOT sold separately.

I can't go buy the Thunderbolt version of my PCIe card without buying Pro Tools 11HD *and* and a minimum HD OMNI $3,000 audio interface. So it's 5-6 THOUSAND dollars to switch from my PCIe card to Thunderbolt. (If sold separately it would still be a $2,000 cost).