There is really no reason to support ppc, unless its an app used in a specified field such as video, music, etc., and it was released for ppc previously.
You may have just touched on their reasons not to upgrade to an Intel-based box.
It may just not be possible to get iFuntastic to run on a PPC-based system. Or the developer doesn't have one to test the app on, or doesn't want to have to support 2 architectures, etc.