Hey Curt,
Turns out, Eric Rohrbaugh was reading the forum today.
The reason the machine marks are left in, to a certain degree, is to show the owner that these are, in fact, cut from solid billets and not MIMed or forged pieces. Eric says your slide is at the extreme end of acceptance from their shop, and if you feel they detract from the gun in anyway, and want them removed, Rohrbaugh will certainly take care of that for your if you send it back. They would re-finish the top of the slide so those lines are not so prevalent.
Eric says in the future, they plan to finish the top of the slide to a finer cut, so as not to bring too much attention to the machining lines, which they thought were not objectionable. Further proof that the R-Bros respond to what folks say about their firearms, take in such information, and act upon it to make the guns better.
Hope this makes you feel better about the situation. I suggest you give them a call next week and discuss it with them.
Thanks.