In order to be DOCSIS 3.0 certified, your modem does have to support 4x4 bonded channels (4 channels up, 4 channels down). But that does not mean your provider has the channels available or will provision them for you. DOCSIS 3.0 modems will happily provision themselves down to 1 6.5Mhz channel down, yielding just 38Mbits as a maximum.
There's a lot more to it than just channel allocation, as well - the 38Mbit maximum for a 6.5Mhz channel is with 256QAM and a good signal-to-noise ratio, which depends on a huge variety of factors.
Plus, even if you're getting plenty of channels allocated and have a good SNR, there's still the backhaul from your nearest point of presence into Comcast's WAN, the bandwidth across Comcast's WAN, and then whatever peering agreements they have to get across to the Internet at large.
At any rate, I think this is a pretty silly argument against Comcast - it's like being angry that your Gigabit Ethernet switch doesn't give you 1000MBit access to some random server on the Internet.
I could not agree more about latency. My first try with Century Link last year had 120ms latency which is terrible because Comcast was 15ms. CL upgraded my neighborhood loop and got to 20ms which is fine, but the CL upload speed is still crippled at an outdated 768kb/s where as Comcast I get 3.5Mb/s upload. I work from a home office so upload bandwidth is important.
So since there is no other contender that has both good latency and upload speed I use Comcast for now.
I work for a telco, we just upgraded all our cable and plant for 13k customers so we could offer 100Mbit down / 10Mbit up. The old max speed was 50/5. The cost was in the millions, even though the modems have supported it for years.
edit: You did say, "millions", but my point still stands. Unless it was 10+ million, which seems like a stretch.
also: You don't have to amortize it over anyone in particular. You have revenue, you get to dictate how that revenue is spent.
Remember, too, that only a small percentage of customers have chosen to upgrade to 100MBit, so you can only amortize it over them. We did the business case beforehand and it didn't really make sense to be honest. We did it to keep the regulator happy(er) (we're not in the US).
