We're talking about total amount downloaded, not bandwidth. The amount of electricity ( read: cost ) used by Comcast is not affected whether I download frequently or infrequently. The reason it is affected, is because they oversubscribe their customers, so when everyone downloads at the same time it causes a bottleneck.
If I'm leased a 1 gigabit pipe, I want to be able to use the entire gigabit pipe for as long as I want. Limiting this with data caps is at best misleading to customers and at worse a scummy business practice.
And while we're here, lets do some math. An unmetered gigabit pipe downloading at the theoretical limit gives you 328.5 Terabytes of data in 1 month. Under Comcast's 1.2 Terabytes per month rule, that gigabit pipe you're leasing is equivalent to downloading 24/7, on a 4 megabit pipe!