I think BW's intention was to present a randomized list of available crafting missions, which changes at each new area. I don't think that's in question. I don't understand why intentionally changing zones in order to reset the list would be considered an exploit, while "unintentionally" resetting said list is entirely kosher. Same exact experience, identical results, motivated by different goals.
Seems to me this is more of a semantic issue than anything else. Out of curiosity, can you think of any other comparable exploits in the game? That is, a mechanic working as intended, but leveraged in a way that wasn't intended by the developers. I'm wondering if I would agree with that terminology in those other cases.
1) I'm not sure what you mean by a 'semantic' issue. An exploit is an exploit, there's no such thing as "an exploit in name only". Intent is difficult (impossible) to prove 100%, but we can easily infer intent by observing people's actions. If your actions serve only to reset the mission list, you are exploiting.
2) Whether or not that exploit is worth BW doing anything about is a different story. In this case, running a single tier one mission barely (if at all) takes longer than logging out and back in or rezoning, so I don't see it really being a problematic exploit. Most people (including myself) would probably get a better ROI by spending the time some people use to log out and back in paying more attention to the market -- I know I could make a lot more money than I do, but I'm lazy and I make enough.
3) An example of something WIA that goes beyond what the devs planned, but that they decided to let go, is using Legacy armor/weapons to pass Bound items from one char to another in your legacy. They said BoL was absolutely not designed for that, but that they didn't care that people use it for that. (As an aside, I consider that an exploit that I wish they would fix, as it essentially lets people gear up fresh 55 alts with BiS (78P) gear, which is why I think we see a lot of overgeared chars that don't seem to know their class in FPs).
Anyway, I guess you could say that I think that it IS an exploit (as exploit is defined), but (since BW appears to know of it and accept people doing it) that it isn't an "exploit" in the sense of something that is "wrong".