What do you mean by "production support for Web Services transactions"?
Last time we discussed someone from Arjuna told us that we should not use it for production because the protocol was far from being optimized and that it was so "verbose" that we would better stick with JTA (more specifically he told us that to do a distributed transaction using web services transactions would imply up to 18 messages between application/transaction service where only 2 were needed if going through JTA/ATS)
It is certainly true that JTS will be quicker than WS-TX and, if that is an option for you, would be a better choice. The main reason for choosing WS-TX, though, is interoperability with other systems, especially those which are not under your control or do not support OTS/IIOP.
There are a few differences between the two protocols but certainly not as great as would appear to be implied by Arjuna. Both protocols must create the transaction context, enlist resources and drive the two phase commit (certainly more than 2 messages).
The main differences between the protocols are the message format (binary versus soap/xml) and the use of one way messaging to drive the WS-AT two phase commit. These do add a performance impact to the WS-TX protocol but the tradeoff is interoperability.