We've been lucky that Castle and AD6 have had the ability to successfully market their hardware outside of the RISC OS desktop market. I'm sure this is core to how we've managed to end up with two excellent hardware offerings available.
Unfortunately for Eyetech they don't seem to have achieved any significant successes in other markets and, in addition to that, Amiga OS 4 hasn't officially been released. So not only were they limited to the enthusiast market but also further limited to those who were willing to accept just to be able to run PPC Linux and (later!) the beta releases of Amiga OS 4. While AD6 said that their beta scheme offering did very well I'm certain that that alone would not have made their venture financially viable.
It's not all gloom for the Amiga though - Amiga OS 4 is pretty much ready for release pending the availability of hardware to coincide with an official release. So hopefully the Powervixxen will be completed soon and there are hints of another hardware solution so it's just a case of wait and see and hope for the best. I would be sad to see the Amiga completely fade away.