99.9% not touching 1.2 TB a month most likely isn't true, but
The $30 is another "upgrade" they can pressure people people into paying for even if they won't hit the cap. They can also use it to leverage people into upgrading to the higher tier without limits, etc.
Comcast probably makes most of their money selling people extras they don't use. There are plenty of paying $300 a month for cable TV that watch 3 channels.
You can hit data cap in less than 2 days. Ask me how I know. I don't think it's true at all either.
And yeah, I paid for HBO for a LONG time after GoT ended...never even watched it. We've also been paying like $10/month for an extra HD Cable box that we've never even plugged in. For like 5 years now. lol