I'm guessing if you get the ESPN channel as part of your base Comcast Pkg, it does not mean you will get ACCN?
ESPN is pretty much included in every basic package, so that's not a good barometer of whether you'll get it.
There are various scenarios:
1) Comcast decides not to carry ACCN (also means not available online)
2) Comcast decides to add it to a their base package
3) Comcast decides to add it to a higher tier package or sports package
The complexity is that Comcast (or Charter, etc) could do different things in different regions. The second option is obviously the best case scenario for customers and GT/ACC. The league gets a certain amount of money per subscriber, so the third option cuts into that potential revenue.
IIRC, SECN took about a few years before it became a part of standard packages across the region.