Well, Comcast was predictably useless over the telephone. They admitted doing a digital cable box upgrade last week, but I couldn't find anybody willing to own up to disabling my serial port. I'm going to have a technician come out just for sh*ts and giggles.
In the meantime, my goddess of a wife was able to find my IR cables which had been put away somewhere for years, now.
Just for good measure, I fired off a consumer complaint to my state's AG office - conveniently enough, perhaps, that the AG, Comcast, and I are all in the state of Pennsylvania. I indicated that this action on the part of Comcast was clearly an anti-competitive measure designed to cripple third party devices and lure less-technical-savvy consumers into having no choice but to resort to purchasing and subscribing to Comcast's [clearly inferior] DVR device/service. I equated it to Comcast potentially doing something like blocking Vonage traffic in an effort to sell their own VOIP solution.
The Borg Bundle (Comcast cable, internet, VOIP, and DVR) hasn't got me yet - still have Vonage and TiVo, at least.