My take on this is
that most people consider NIW as working in national interest area. Its not like that. Its waiver of the labor cert. which inherently is of national interest. hence the term NIW.
It also means waiver of job offer requirement. Hence no ongoing job is reqd (although its best to have one).
I have not done EA, so I cannot comment on it. Suryasaha, you have OR and NIW approved, so you might know more about EA/OR (as you might have looked at both).
For an NIW, your work needs to have substantial intrinsic merit, be national in scope and the all important ---your background and your importance that can allow the waiver of job offer and also supersede requirement of LC.
e.g: since you are a geneticist, if you work on chromosomal alterations having implications towards trisomies and then you leave job and work elsewhere on chromosomal alterations or dysjunctions etc again..then you are good. Thus you only need to work in your area of expertise. this is what I got from this and murthy forum.