There's no way of telling how many of those Netflix subscribers are getting their movies through Comcast, but it's certainly a significant number. Let's assume they all do.
Let's also assume they get the 2MB/sec to 4MB/sec generally accepted as the average Internet access speed for cable connections, which is largely supported by the latest FCC national broadband report (PDF).
This Netflix bandwidth analysis pegs its single-user Internet hoggery at 56.3MB/min, or .93MB/sec.
Some less metric-intensive, but savvy users estimate Netflix movies at about 1GB/hour, which translates into 16.7MB/minute or .28MB/sec.
Actual bandwidth depends on the size of the picture and compression; here's a relatively technical explanation from Netflix' CTO.
Compare the higher number -- less than 1MB/sec, with even the lowest Comcast service level of 1.5 MB/sec downstream and it's clear Comcast actually doesn't have a case.
In most households, only one person watches a movie at a time. In households with only 1.5 MB/sec Internet service, it's certain only one movie is on at a time. What remains of that household's bandwidth allowance could be eaten up by Farmville or email or IM, but there's no way two people would try to cram two movies through that tiny pipe at the same time unless they like watching freeze frame.
So Comcast does not have a case.
Even if every single Comcast user was also a Netflix subscriber, the movies alone would not push them above their bandwidth usage limit, and would not overburden Comcast's backbone or edge network unless it was a lot less substantial than Comcast has promised customers it is.
Of course, during the elections in November Comcast's digital voice network got swamped by political robo calls, which is a big, stupid flashing sign that the network itself is build on silly string and broken promises.
So if Comcast is telling the truth that Netflix is overburdening it, it only has itself to blame for shortchanging its customers in the bandwidth it provides and the promises it makes.