I think you are correct to blame TWC. In fact, seeing as TWC has already admitted to blatant "packet shaping" (even in non-abusive users) it wouldn't surprise me if they are intentionally screwing with online video as well. Which is why everyone who is loving their Roku boxes should donate a buck or two to a "net neutrality" organization of their choice. The cable companies/internet providers would like nothing more than to see online video fail. After all, it cuts into their bottom-line, I personally canceled my cable this year and rely on netflix and roku for my TV viewing needs. Despite what you may see on the news, net neutrality really is about the future of online video (everything else is a distraction).
Incidentally I own 2 roku boxes that I have viewed over 100+ hours of content on. One of my boxes gets a poor wireless signal (its in the basement, so I've had to lock it at "2 dots") but the other box has never connected with less than 4 dots and both have never locked up or re-buffered no matter what time of the day (then again I do have the FIOS 15/5 plan). The only issue I have had was when I got my first box (in October) it took an inordinate amount of time to successfully access my netflix instant cue. However, since then, they have been fine.
I am giving one of these boxes to my family tomorrow as a belated Christmas gift (and replacing it with a new one). That way I know for sure they are getting a functioning unit. They have TWC so it'll provide a bit of a "test" to see if it is really is the cable companies who are dropping the ball (intentionally or not).