I'm already through with few tests surveying npots support on ati x1x00 and here are conclusions:
-you can specify any non power of two texture size and use it with mipmapping and auto mipmap generation(texture filtering allowed)
-you can't use any of REPEAT wrap modes for such a texture

And now let me quote:
"An implementation which supports relaxing traditional GL's
power-of-two size restrictions across all texture targets will export
the extension string: "ARB_texture_non_power_of_two".

When this extension is supported, mipmapping, automatic mipmap
generation, and all the conventional wrap modes are supported for
non-power-of-two textures"
(from ARB_texture_non_power_of_two extension specification)

As not all conventional wrap modes are supported, its not fully compatible with specification and this is why the "ARB_texture_non_power_of_two" string is not exported, which doesn't mean you can't use npots in, for example, postprocessing where GL_CLAMP_TO_EDGE wrapping mode is being commonly used.