Well, as the new DOCSIS 3.0 chipsets can support the bonding of up to 24 downstream channels, the CMTS vendors need to be able to support that too.
Also, as was stated in that Light Reading Cable article (»www.lightreading.com/document.as ··· lr_cable
And, according to this statement from Comcast spokesman Charlie Douglas, it appears that Comcast will use the fiber-based approach as a placeholder for very high-capacity residential broadband services until it makes business sense for the MSO to make significant changes to its Docsis platform:
"We've demonstrated our Docsis 3.0 infrastructure, which we currently deliver to more than 50 million homes, is capable of delivering 1 Gbps or more. While demand for faster speeds continues to grow, demand for ultrafast speed tiers (of more than 200 Mbps) is still emerging. In the near-term, until there is clear demand to modify the capacity of our existing Docsis infrastructure, we can provide our new residential Extreme 305 service by leveraging the fiber already in our network and our Metro-E product."