Textures that you create are as yours are images you create in Photoshop. Probably even more yours than that ;)
My doubt is about authorship. If I make a texture with texgen, can I claim to be the author? Probably yes, but where do we draw the line? If I create a Minecraft world by selecting a single seed, and take a slice of the world as a 2D image, can I claim authorship? What if I didn't even change the seed, just pressed "create"?
I think it depends on the country, but thinking about authorship over procedural generators is weird.
I couldn't claim authorship of a machine generated work. I would feel better about claiming authorship of something I've spent a while working on and finding combinations until I get something I like.
Do you claim authorship of Photoshop's cloud filter?
Where do you draw the line? If people can copyright a bunch of settings, does that prevent people from using the generator with randomized parameters in case they accidentally hit a lawsuit?
http://en.wikipedia.org/wiki/Threshold_of_originality
As an example: if I use a seed to create a grainy texture, it probably isn't original. If I use the same image as a grain filter for a photograph, the result may be original (in a legal sense). Both operations are trivial and just a click of a button (or two), so I think the discussion about the ease is moot in that context.