For some reason when I used forum search, I didn't get any of these results before. I may have been looking through the wrong area at the time. Regardless, it seems that the post Lee Jackson made received an answer that explains what happened. In fact, Lee's reasoning is the same as mine: a quick and dirty way of prototyping a work in progress. I installed VirtualMIDISynth and put in a GM2 soundfont, and it's not doing anything for Cakewalk, so it doesn't help my cause. I'll look into TTS-1.
Edit: TTS-1 is for Sonar users and/or special versions of Cakewalk. That option seems to be out for me. Even if it's legacy or whatever, I really don't understand the need to purge the only built-in MIDI device.