This is why the Elf rings are more powerful, and have names, and not-coincidentally have not led their owners weeping and screaming to Sauron's doorstep, as the other sets of rings have done.
There's alos the point that Sauron had no part in the forging of the Elven rings, and therefore they were not corrupted, whereas the 9 (for Men) and the 7 (for Dwarves) were. Apparently, the 9 allowed the men to gain power, while the 7 enhanced Dwarven fortunes. The Dwarven rings also increased their greediness and xenophobia, IIRC.
Did Tolkein ever explain, in the books or his letters, why so much power was put into physical objects, rings?
That's straight from the Norse myths he drew from. See: Ring Cycle by Wagner.
Tolkien actually hated comparisons to the Ring of the Niebelung. (Although it is an obvious comparison). In one of Christopher Tolkien's History of Middle-Earth series, Morgoth's Ring, I think there is much discussion about rings and power, although I haven't really gone through the volume myself. (Morgoth's Ring was Arda (the Earth) itself, meaning that Mogoth had his power tied to the physical world).
[Edited to add that one of the themes in Tolkien's work was binding power to physical objects, manifested in the One Ring and why when it was destroyed, Sauron disappeared.]