Shoot the gun and do not worry about it. It is not meant to be a high end, high priced gun. But if it really bothers you then call Ruger and see what they will do about it. The only thing they can do is issue you a new gun and depending on where you are that may or may not be a hindrance.
I have my second SR1911 Commander. Ruger replaced the first one, the second one isn't as good as the first, both shot low, the replacement shot low and the bbl didn't lock up tight at the bbl hood. I Sent it back also. They installed a long link to repair the lock up. They don't regulate the sights altho they do claim to shoot to make sure the group size is within their limits. I filed the front sight down .030" to zero it.
Shoot the gun and if it checks out don't do anything to it. Also, my gun has the same cut on it as yours.
In the machining world we call this a "false start". Either the tool length was set wrong or the tool pulled loose from the holder during the machining. I have several friends that own Ruger's. I think Ruger will make this right for you.
My full size sr1911 also has a notch like that. Although it's on the opposite side and not quite as distinct as the ones in the photos. I didn't even notice it until I read this thread.
Damn why did I read this! I won't sleep at night now