I'm not doubting they actually give you a gigabit connection, but especially during peak hours, I doubt the transit links you hit would necessarily have that much to spare.
For doing backups/restores, in this age of multi-terabyte disks, fast network links (especially in the upload direction) are a necessity.
I don't mind some oversubscription, I can work around peak hours, hell, I'd love to temporarily trade away most of my downlink bandwidth in exchange for uplink bandwidth -- average upload speed is all that matters for this sort of large transfer.
Compounding that, the latency comcast deliberately introduces into their network (I've got many ISP's to judge on here) makes the internet ugly, but only if you don't pay for their services.
What we need is not a target for faster downstream, but higher competition - I could give a shit about network neutrality if the providers offered network honesty: a 500 GB monthly limit is a 1.5mB stream - full stop.