Thanks for moving this to the right forum.
I did some further digging and found Orbitz does not offer a premium economy option either. But strangely, Zuji.com, which is Travelocity's offshoot in Asia, does!
Odd that Travelocity does not offer this on their site then. I guess no US airline offers premium economy for sale yet, so that may be part of the reason.
But so many major airlines outside the US offer it now (BA, Virgin, AF/KLM, Qantas are the ones that jump to mind; SQ too until they decided to get rid of it recently and make their A345 aircraft all-business class) that I think it would be a good feature to add.