What Indytower means is,
All of these feeds are voluntary by individuals in most cases, done by ATC/Aviation enthusiasts at their home computers, using their own scanner equipment. Most do it to share their local ATC communications for the enjoyment of the hobby.
So likewise not all computers hosting the feed can be up 24 hours 7 days of the week, sometimes due to situations beyond their control (i.e. weather, pc problems, etc.)