The document shows that it is configurable within WL and shows the reason why (which is what I had previously discussed). There is no one "correct location" to enforce this policy. It is often easier for sys admins to manage this within the TM configuration, particularly in a distributed environment where different interposed coordinators can have different runtime configuration options such as this. Furthermore, not everyone has the ability or the capability to add new XAResource implementations and ensure they are picked up (and driven correctly) by the application server. This does not have to be a global setting: it's configured on a per instance basis - different runtimes can see different values, which comes back to what I said before in the context of interposition.
We can debate this for ages, but I want a configurable option for this. I believe there are good reasons for it and you have yet to prove that the absence of a configurable option is superior to its presence. Yet another benefit is the fact that customers migrating from WL may be using this option within their applications and expect it to be honoured.
I find it ironic that you used the argument "WL does it this way so we should too so it must be right" for the calling pattern, and yet don't accept the same argument back