Point taken, but I think it is a matter of definition. Let me rephrase. It is impossible to implement synchronous communication without some synchronization mechanism, and thus entirely asynchronous systems cannot implement synchronous communication.

This statement may be entirely obvious, but I think that is only because thought has been put into properly stating the issue. More to the point, what I am actually trying to say is that the original post seems to imply that settling on synchronous communication is somehow more limiting than settling on asynchronous communication, and that this is false.