Wow, I figured this was just a bad day vs. SOP.
To add a little more context, this was a regional crew scheduling issue -- right before the phantom delay, the GA for the flight to Ottawa (across the concourse at C6) made an announcement that "our flight attendant and first officer have arrived, but they believe they're supposed to go to St. Louis. We'll get this sorted out, and get back to you right away." That was the first indication that this was going to go awry.
My original flight eventually cancelled, after being delayed further to 10:25... glad I chose to head into the office.
As a wonderful finale to this, I shot UA a quick e-mail that was more or less a cut & paste of my OP.
Their response:
Hello,
We have received your email and are working to respond as quickly as possible. Our current response time is 10 days.
Sincerely,
United Airlines Customer Relations
/ugh