It has alot to do with who owned the system prior to Comcast and any deal that Comcast had to make to get a local franchise agreement approved upon takeover. I noticed in many of Comcast's current agreements that they had to take 550mhz systems to at least 750mhz in some cases and others only to 650mhz. I think the system that I am on had to be taken to 750mhz from 550mhz by September 2004 or something like that for example.
I don't know what makes New Haven special other than luck of the draw.
I'm sure it sucks right now not getting the new channels that Comcast has added and have no idea what their plans are for upgrading systems. I know I'd be very frustrated reading about systems within a hour of me getting channels that I couldn't.