Am I not understanding something here?
No, you're "spot on." The data is collected using different test barrels or revolvers, which can give varied results. Maximum loads should always be worked up for a particular gun, with the book loads being used for general information only.
As an example, I once had a Thompson-Center, 10" barrel that was chambered in .38 Colt Super. I soon found that loads that were more then safe out of a 5" Government Model ran excessive pressure levels in the longer TC barrel when using certain slower burning powers.
In the present instance the extraction problem could be caused by a number of things (or a combination thereof); but before jumping to any conclusion some different ammunition and load-levels should be tried.
If bad chamber(s) are behind it, Ruger should replace the cylinder. Then, and only then, consider polishing. Generally speaking, a correct chamber that still has reamer marks will not affect extraction.
In some semi-automatic firearms the chamber is actually threaded to delay extraction, but never the less does not prevent it. Ruger's revolver chambers don't come remotely close to this.