I have this idea that Honor's power (which should still be in effect) is somewhat contract based, if that makes some kind of sense.
For example, we have the "Oathpact" - maybe in return for power/immortality they had to go through hell. Maybe that's why the ones who didn't go back to hell left their super swords? Maybe so long as one was in hell, parts of the contract would still be valid?
Kaladin's "Words" (note the official-like capital letter) aren't quite so powerful, but they still indicate some kind of commitment - and in exchange Kaladin's power becomes more refined. I doubt there's anything inherently magical about the words - more about setting up an exchange, or something along those lines. However, I think Syl would have had to have been there.
Anyway. Just an idea. It may even be partially correct. I certainly would expect there to be much more to it.... which we'll find out in later books. This is going to be a long series, so we're not going to find out everything in the first book.