It almost sounds as if some people think the Teron CX's sold via different distributors (like Eyetech and Terrasoft) are different. "Amiga compatibles"? "Another PPC motherboard"? It's the same motherboard.
And what's this supposed to mean: "Pricing similar to the AmigaOne, but graphics support in Linux limited to AGP 128 Rage Pro"? Whatever drivers exist in Linux naturally run under Linux regardless of whom you buy a motherboard from!
Included in the $500 is of course Yellow Dog Linux, which otherwise costs $60 when bought directly from Terrasoft, including 2 months installation support ($30 with "normal" support).
Unless the distribution policies for AmigaOS are changed, it's all moot anyway, AmigaOS users are not allowed to choose their hardware vendors freely. Like I've said, the market for one piece of hardware has been turned into two separate markets - "hardware allowed to be bought by AmigaOS users" and "hardware for everyone else".