Some gunmakers will round the back of the butt as a special option. It;s supposed to help with recoil so the butt doesn't dig in your hand, and some like it for CCW. I think it looks interesting, but wouldn't want it done. First of all, if you didn't like it there is no way to revert back, and I think it might make the gun harder to hang on to. Others who actually have a gun like that might tend to disagree.
btw, this is off the subject, but does anyone else see ads about girls in swimsuits, and ads for getting you're teeth whitened ? Seem a little odd on a site like this.