Is it really necessary to plug all your receivers and the Slinglink directly into wall outlets? If so, that is crazy. Who in their right mind won't protect their DVR and connected equipment from power fluctuations? I have a power conditioner with voltage regulation and a UPS for each of my ViP722s. Aside from frying your equipment, one dip in power and your hard drive could be wiped clean. I wouldn't dare expose them to damage. I just got a Slinglink W1 from Amazon tonight (the same one that is on the Dish website). I plugged it into my power conditioner. The ethernet cable was connected between it and my router... and the router is also plugged into the power conditioner, too. Just as the OP noted, no dice. Very disappointing.
There are supposed to be some UPS or power strips out there that do condition the line but also permit Ethernet-over-power to transmit. I have not actually seen or tried any of them, though, but I know I have heard of them.
I had posted that I thought the Ethernet-power-adapters had some sort of power protection, but I could never find any proof of where I remembered reading it.
I understand the desire to protect your equipment... so it is basically a trade-off of whether to protect your equipment OR use a convenient method of internet connectivity.