As a long time (6 years) and now former cable modem owner I can assure you a UPS on the modem is not going to be much help. After any kind of storm the whole cable service is down for a day or two and the "data" won't be back for a week or more after they get the TV going.
I finally got frustrated and took the slower DSL since when averaged against 12 hours of "zero", .9-1 mbps is faster than the 1.6-1.7 I got from the cable 6.5 days a week. (and totally dead for days after a storm).
Cable would have to actually have to work for a week or more without an outage before I would ever consider dumping my POTS phone for VIOP. So far I have not seen it. I do hit it pretty often since the weather station at my house updates my web page once a minute. I can look at my log and see when it is down. I reported this to Comcast and they just blew it off. Their definition of "down" is you didn't swap ONE packet in 24 hours.
I sat their modem on the front porch in the DSL modem box and told them to come get it.
