It wasn't a modem firmware update that caused the problem. It was a CMTS software update to meet updated DOCSIS 3 specs that wasn't compatible with older 6120 firmware, specifically version 220.127.116.11.
The bigger problem was Motorola was still distributing version 18.104.22.168 in it's retail modems several months after the problem came to light (22.214.171.124 was over a year old at that point, the new firmware release on retail after Moto acknowledged the problem was 126.96.36.199). The 188.8.131.52 modems wouldn't sync on CMTSs with the newer software, but the modems weren't bricked. TWC or the other cable companies couldn't update them normally since they wouldn't sync. TWC had updated the 6120 modems on their network before the CMTS update. I'd guess this is why TWC doesn't officially support new customer owned 6120s on their network, since there are still ones with 184.108.40.206 new in the box wandering around. 6121s had newer firmware from the start.
This hit all the MSOs: Charter, Comcast, Cox, BrightHouse, Optimum, and TWC all had threads about the issue here on DSLR:
»[Connectivity] Motorola SB6120 doesn't work with CC-Resolved
»[AZ] SB6120 Provisioning
Many mistakenly thought it was a ISP modem firmware update failure since Motorola never said anything about it publicly. ISPs just had to deal with the fallout and old stock of 6120s ever since. Even Karl misreported it: »Firmware Update Cripples Some Motorola SB6120 DOC 3 Modems
If anything, TWC learned to update customer owned modem firmware more often. As far as I know TWC does update customer modem firmware, when they update other modems of the same make and model. It's can't be requested from customer support, they can't do it, most don't even know how it's done so you get a bunch of odd and wrong answers about it. Modem firmware updates are pushed by an automated process initiated/scheduled by TWCs Engineers.
BTW, the majority of 6120 modems I've seen in my area on TWC are running firmware 220.127.116.11. Retail modems never shipped with that. It was released Aug 2011 by Moto and mid last year by TWC. Motorola has averaged a new firmware for the 6120 every 2-3 months for almost 4 years now, most ISPs are 3-6 months behind at best and none I've seen push every release. The latest I've seen is 18.104.22.168 released Dec 2012.--
Two is one, one is none. If it's important, back it up... twice. Even 99.999% availability isn't enough sometimes.