Twonky is a DLNA media server. DLNA is a well-established standard that's been around for years, is supported by thousands of devices, and works pretty well.
If Amazon choose not to support it, or apps use their own proprietary media streaming protocol, that's not the fault of DLNA or Twonky. It's squarely at the feet of Amazon, as, Bennor suggests, trying to force users to buy their media streaming services. And, as you point out, they are getting us to pay for shopping portals.
Well, not me, as i won't pay for a shopping portal, and told them to stick the trial of Amazon Prime as I couldn't run it on my Android tablet, and they seemed to expect me to buy a Fire just to use Prime. They can GTF.