Yeh.. But you can use those textures as stand-ins, and use the Gimp or whatever to make your real terrain textures.

I'm in the process of trying to learn Terragen for all this, though, after seeing the quintessential (for RPGs anyway) green hills and blue sky with perfect grass and flowers. Call me stereotypical, but there are just some things I want in my game. My first one, at least. :-)