Well, being that it is the DOCSIS standard, I guess that's just the way it is. Does the spec say anything about the ISP being responsible if the modem gets bricked? I can imagine calling Comcast with, "Your latest firmware broke my modem." Considering even the simplest problems can take multiple calls and escalations to resolve, I'd hate to be the complaining party on that call. But, hey, I lease my modem (eMTA), so my path is clear. And I haven't heard of anything like that happening yet, but give them enough time and enough modem models...
"Whether a cable modem, gateway/router, voice capable modem or other device is owned by you or us, we have the unrestricted right, but not the obligation, to upgrade or change the firmware in these devices remotely or on the Premises at any time that we determine it necessary or desirable in order to provide Service(s) to you in accordance with our specifications and requirements."