I think one of the problems resellers may face is security. You can almost fully control how much time, or money, you put into a business, as well as customer service levels to provide your customers. However, many of our customers that come to us have come from web host who didnt have the proper security, exploits were ran and websites defaced, etc. Not having full control over there server is something that limits how much of a reliable service they can really host. You can only be as good as the man infront of you, and many of the resellers out there face this problem on a daily basis. It's something that may seem far fetched, however, one of the primary problems I have seen many resellers face in the hosting community.
James