According the spec here: http://groups.google.com/group/json-rpc/web/json-rpc-2-0
more specifically, this section:
If present, parameters for the rpc call MUST be provided as a Structured value. Either by-position through an Array or by-name through an Object.
To me it seems obvious that both styles must be supported, however I've filed a bug report and another developer feels that it's up the developers to decide which method to support, and that the spec doesn't require both.
I can't find an official answer, other than what I quoted above, which the other developer doesn't interpret the same way I do.
So, what is the general consensus?