And if you do get suspended out of the blue? Best option is to just use another ISP -- even if Comcast isn't willing to support people who use tons of bandwidth, there will likely be another company that does. And if high-level broadband does become really widespread, it would be a bad business decision for Comcast as well to suspend large numbers of their userbase -- while there's always the chance that they could start charging a premium for more bandwidth, smaller companies will likely step up to fill any spaces that Comcast tries to screw over.
In short, right now, this isn't a problem. While in the future, Comcast may try to bring the bandwidth cap lower and lower, at this point, it doesn't effect enough people out there to worry, and even if you are affected, there are likely steps you can take to get around it, including going with another ISP if that's an option.