I don't think that the issue is specifically related to an overtorqued barrel so much as it is related to a fairly tight interference fit between the frame and barrel threads. It is just how Ruger does things.
The jist of the problem is that you create a slight constriction in the barrel just ahead of the forcing cone (right under the barrel threads). For most shooters it never presents any issue, or they are simply not anally retentive enough to bother with it. However for those that are enthusiasts, very particular about their gear, or want to shoot cast lead bullets without barrel leading, it can be a problem.
Shooting lead bullets requires the correct fit between the bullet and the bore (typically the bullet should be .001-.015 over bore diameter). The thread choke constriction sizes the lead slug down as it passes through. Now, you have an undersized lead bullet which no longer perfectly seals the bore. Some of the hot chamber gasses bypass the bullet, melting the lead and allowing it to deposit in the bore. Once that starts, it is a downward spiral to more leading and reduced accuracy.
With copper jacketed bullets you don't have the leading issue so the problem is likely to go unnoticed.
As mentioned, fire lapping is the generally accepted method of getting rid of the problem, and has a few other benefits.
You take a 100% pure lead, unlubricated and unsized bullets and roll them in a mild abrasive, typically 320 grit valve lapping compound, imbedding the compound in the driving bands. These bullets are then loaded over very light charges (just enough to get the bullet out of the barrel).
When fired the bullets travel down the bore and will hone away the tight spots (more pressure = more metal removed). In addition, as the abrasive bullet travels down the bore, the abrasive will wear away, meaning you have more honing action at the forcing cone end than at the muzzle. This leads to a very slight taper in the bore from forcing cone to muzzle. This taper also benefits lead bullet use by continually sizing down the bullet as it travels, ensuring the gas seal is maintained.
Lastly the abrasive polishes the bore (both lands and grooves equally) and will leave the bore with a mirror polish. All tool marks and other imperfections are honed away.
Once completed, and with a correctly sized bullet to begin with, your gun should now be able to shoot lead bullets both accurately and cleanly.
My 44 Mag Super Blackhawk Hunter had this issue when I purchased it, and would lead the barrel in 20-30 rounds. After fire lapping I can shoot lead bullets all day in that gun without so much as a speck of lead being deposited in the bore. Another advantage is that the mirror bore requires almost no work to get clean. Literally 2 patches is all it takes to achieve a clean bore.
