I like dahenny's answer best. I don't believe it's Dish's responsibility to wire up the Ethernet jack when they do (i.e. pay for) an installation. They certainly don't supply a HomePlug bridge to your wired network, nor do they fish cat5 cable through attic, walls, or crawl space to get to your router that way. So why should it suddenly be Dish's responsibility to set up a wireless link correctly, when they don't hook it up at all via any means?
I can't contradict anybody's explanation of the support problem from Dish's point of view. I'm just saying it's a bogus reason for not adding dirt-cheap wifi adapters inside current generation receivers. The HomePlug adapter costs more.