Well, other than the rules kind of being a pain in the neck about that, to keep players from having every ring in the DMG implanted in their body somewhere.
Early on in our games, we decided that the "standard" locations were that way for a reason -- and the justification we came up with was that the magic interacted with your body's Chakras
. Overloading/disrupting one's Chakrahs (say, two rings on one hand) usually caused increasing discomfort until death, along with non-functioning of the items (neither was able to draw sufficient energy to operate, but both were causing damaging feedback). Location was a factor, in that one could wear two rings (or a bracelet and one ring) if spread over the two arms. Earrings, however, were too close to your Brow Chakra and so you could only have one magical one, etc. Armors almost always tapped into your Root Chakrah (so no wearing rings/bracelets on your toes/legs if you also wore armor, etc.)
A little cheesy perhaps, but it put to rest most of the usual questions/complaints while also providing a framework for cute character customizations that were not unbalancing...