Comcast isn't doing this for today or tomorrow. They're doing it for years down the road. "99% of the customers do not use over 1TB", so why bother? Well 5 years from now, 10 years from now ... you'll be using significantly more bandwidth than you are today. By then the cap will be common place, people have long accepted it, and that 1TB cap will not seem like a lot of room. At that point Comcast can really begin to monetize a cap by charging a lot more for data.
Compare it to that free cloud storage. 5GB of iCloud may of seemed like a lot several years ago but now it's barely enough or not enough for many users. Same concept. Give people more than they need so they think it's OK then in the future really clamp it down on them by not raising the 'free' space anymore.
Don't forget back when Comcast did the original bandwidth cap (250GB) ~2009-2010 that lasted only a couple years, they were claiming the average usage was 5GB. The averages spiked to 34GB by 2012 and are now around ~56GB in 2014 and it's climbing quickly. Now that internet speeds are at a point you can take your entire household off of Cable television and stream online we're seeing massive increases in that "average usage" that Comcast loved using to justify the original cap of 250GB, year over year. It was a racket then and it's a racket now. Comcast claimed they would increase the bandwidth limit as things grew but if you just analyze the original 5GB usage in 2009 to 50GB in 2014 there was a 10x usage increase. That means the cap, if growing with the usage was accurate, they'd put it at 2.5TB to represent 2014.
People like to nitpick over usage patterns of some users, but it's always following the ISP's narrative which is complete BS and should be disregarded. The meters are inaccurate. The price gouging is inexcusable ($50 more for unlimited or pay up to $200 in fees? Cell phone model) and most people would probably take throttling over fees if it really was about limitations, which as a Network Administrator I can tell you is how you'd solve bandwidth issues. You either increase the amount available or prioritize traffic and limit users. How they can get away with absolutely lying and deceiving their customers and the federal government shows how corrupt our system has become.