WS-Transaction, as currently spec'ed, is based on SOAP. There is nothing preventing a similar facility being designed with HTTP headers in mind, but that work hasn't been done yet.
It is also worth noting tht WS-Transaction comes in two flavors: tightly coupled (Atomic) and loosely coupled (Business Activity). Much of the focus in the WS-* world is on the tightly coupled version.
To elaborate on what Sam said: in chapter 8 we give a RESTful system for non-distributed transactions. I haven't done the work (I suspect nobody has) but if you have a number of different systems that support transactions, you should be able to add some infrastructure on top and orchestrate them with a RESTful atomic transaction.
We didn't cover atomic transactions in detail because Sam prefers the loosely coupled transactions of WS-BusinessActivity. In chapter 10, probably in the ToC section you found interesting ("Transactions"), we show how to implement the WS-BusinessActivity ideas with asynchronous operations (which, in turn, are covered in chapter 8).