The speed of the the internet is not a metric of the plant. In fact HSI only take up 1% of the total bandwidth.
What you need to know is how much the amp and taps are rated. For example CV is has a 870 MHz system using 1gh taps.
If you are referring to a an old Adelphia system then that is one that was neglected and has very large nodes. In fact I would not be surprised to see maybe 1500 homes on just one.
It really depends on what the plant and system is and how it is configured.
But the moral is that eventually it will be upgraded to provide new capacity through more node splitting amp upgrades etc and you will get the missing channels and services like digital voice, HDTV and IPTV.
Dish network cannot provide less than the full suite of premium packages because eventually churn will become so great they will have a problem. Sports and movie packages are the killer apps for programmers and constant improvement has to always be made.