Nowadays, many things in GWT require that it gets access to the compiled classes for your client code, so it's more a packaging issue (it's easier to package **/share/** in your WAR than to selectively pick only some classes from your **/client/** packages) than a compiling issue.
AFAIK, the projectCreator predates the common usage of a "shared" package, that's probably the reason it still generates the RPC in **/client/**.
It should be a relatively easy patch, so if you want to contribute it, do not hesitate!