I think that's a perfectly reasonable response, and even if it takes a few weeks to get the RAM, I don't see that as a problem. In fact, I would rather get my 8204 on Wednesday with the wrong RAM, then be able to exchange, than wait a few more weeks (as some vendors are doing) to get the system at all.
Of course, Acer could change their specs and/or make sure their resellers are communicating the right specs, and then they could even sell the units with PC2-4200. It's just the lack of accuracy that's a problem.