The WD Live is hardly a viable or supported platform. It's flakey and outdated. The Roku is what's current. Promoting a WD Live Sling app is like promoting a Blackberry or Palm app. The issue here is Dish is not "modern" because they don't have a Sling app that can just stream directly from the Slingbox.
I wouldn't call it flakey. My WDTV Live SMP's are newer than my Roku's and work perfectly fine with a Sling350. It's not for everyone, but anyone with a decent home network it works fine. I use one in my home office every day, instead of a having another receiver fee.
It works great for out of home if you have the internet to support it. I stream from Oklahoma to Nevada with it for several hours a day every other month when I go to the Condo to work with my West Coast clients. It looks great on a 60in LCD, but you need at least a 10MB upload and 15 to 20MB is better.