I finally got a reply from Janty on the use of the resistor and here was the response:
yes there is a resistor inside adaptor to protect the dura atomizer against damage because the output is from 4.2 to 3.3 and not like dura 3.3 constant.
...
Dura batteries only put out 3.3 volts?

Yeesh- I'm gonna have to grab a multimeter and verify that- I had no idea. I wonder if it's the same on their mega batts?
Edit/add: Tested a Dura battery and a Generic mega, both fully charged. Both read 4.2 volts.
Sounds fishy- but given the benefit of the doubt, maybe the person is trying to say something they don't know how to describe- like the little dura batteries drop to 3.3 under load or something but the 10440 doesn't.
It may be, too, that Janty atomizers are made with a different coil than Joye's- I think I heard that somewhere, but someone else would have to verify- and the Janty atomizers can't handle the standard 3.7 volts (?), where Joye's can.
There is an actual answer somewhere in all this- I'm kinda leaning toward the one where they limit the atomizer to keep warranty expense down, but I dunno. The stick is just peachy with an 801- but for a 510 solution, elsewhere is probably better if this stuff is not "standard" configuration - i.e., 510 atomizer+3.7 battery. Now I'm not sure whether I can use Janty atomizers on other platforms?
In fairness, I've been using my janty stuff since April, and I have yet to have an atomizer go dead. People pop 'em all the time, from what I read. I've run a janty atty on an 18650 mod, and they haven't shown any sign of dying either. I'm confused.
In fairness too, Janty advertises this as a 510 adaptor
for the J-Stick, not just "a 510 adaptor". If they feel it should have a resistor and behave in a certain way for whatever reason, they have every right to engineer it in the way that adaptor would behave best, in their experience and estimation, with the Stick. It would be easier to just say that rather than this voltage explanation- unless there's something I don't get. I don't think so, but never say never. My expectations were just different, that's all.
Joye's adapter doesn't have a resistor and it's way cheap, so there are alternatives if you have an out of warranty stick and want to try something different, so I'll chalk it up to experience, and use the stick for my 801's as a stealthy vaping unit.