Eventually down time is inevitable no mater who you are or who your host is. From hardware failures, complete data center outages to natural disasters, no one is completely immune to it. It how the down time is handled that sets others apart from the rest. Some have specific plans in place to deal with it while others just wing it.
Some down time is created by the hosts them selves, over loading servers, keeping bad clients, not securing their servers or cheaping out on hardware or network connections.
Alot of these hosts that have frequent downtime are focusing more on growth then customer loyalty. Customer loyalty only comes with providing good service. A happy customer will gladly pay 3 or 4 times as much for a service if they get what is promised.
Just my two cents.