That's really funny, I was actually thinking about that blog post and considering a dash to the airport and back to potentially save the change fee. But my place is in Shenzhen across the border, and that would have possibly entailed losing a day of productivity plus the annoyance of having to trek across Mainland-HK immigration and back if I couldn't get on a same-day flight. I figured they might have been likely to put me on the same day direct flight HKG-ORD a couple hours later, but I was unsure of two things, even though I had read that blog post a few weeks back:
1. I have lost the upgrade and probably been in economy, and possibly would not have made a same-day flight at all
2. Is this supposedly official flat-tire policy written down anywhere by United? I would not enjoy the prospect of trying to convince an agent in the US, much less HK, that something I read on a blog meant I should be put on the next flight standby without a charge!