Thats the most stupid thing I have ever seen.
Its nothing more than confusion on part of the customer. I can't tell you how many times my UPS driver has had customers try to return Dish boxes from him that have the Fedex label on them, on the assumption that if UPS delivered it, then UPS must be the ones to call to pick it up.
Besides that, as a retailer its a pain for me to call Fedex to do a pickup, where as UPS stops by everyday.
It makes absolutly no sense to use 2 seperate companies, as im sure UPS or Fedex would be glad to make some sort of deal with Dish for all of their business.
The only thing I can think of that its easier to tell what direction the package is on. If its UPS its going out, or Fedex if its coming back.