I agree that if people are over-selling their resale servers, that can be a problem. But other than that, there isn't a lot of difference. The bottom line is that if something physically were to go wrong with the server, it doesn't much matter if it's being fixed by the person who sold you your hosting, or the person who sold the hosting to them - as long as it gets fixed.

Many resellers are great website and hosting managers, are very helpful to their clients for all the every day 'little things' that you need from a hosting provider. Do they all need to have the technical know-how to actually fix the hardware? I'd rather go with a reputable reseller who focuses on the things they do best, while allowing the actual physical hosting company to take care of the hardware in the way they know best.