It is that way because package names changed when ajax4jsf was merged with RichFaces.
If you are using RichFaces 3.1.1 or higher then you need to use the RichFacesClient instead of the Ajax4JSFClient. RichFacesClient does extend Ajax4JSFClient but it overrides the relevant methods so it can find the classes in their new packages.
If you were using Ajax4jsf 1.1.1 then the plain Ajax4JSFClient will still work. But if you are using RichFaces then always use the RichFaces client.