Well, I uninstalled everything and followed the full instructions for installing the Mojo SDK on my Macbook Pro with OX 10.4, and it appears as though I am SOL for now.
Unless I was drunk when I first went through this process a couple days ago and have completely forgotten what I saw on the various download pages, the information about what OSX will install the Mac OSX Version of the SDK has changed (see screen shot below).
There is (now, at least) a qualification listed on the SDK download page that indicates the Mac version will only install on OS 10.5 or higher. Ah, well. It looks like, for the time being at least, this user will just have to enjoy Pandora, Tweed, and Fixter and wait with the other kids for new official apps to emerge.
Please don't let my trouble keep the rest of you away. Those of you with operating systems that aren't as ancient as mine should find your inner geek and try it! Instructions for noobs are here. Here's wishing the rest of you better luck. Happy homebrewing!