Private sector vs public vs nonprofit

[Anonymous]

I'm looking for my next "opportunity" and want to check my thinking that at least in some industries, given certain core level of industry knowledge, a project manager level professional could work at a (all in the industry) nonprofit OR private sector company OR public sector organization.

Aside from the obvious pay and cultural type differences, do people agree that the lines are blurry enough between these sectors that it's almost indistinguishable whether the organization is in one sector or the other? Or do you think that there's enough difference between work in these sectors that a professional careerist needs to develop sector-specific skills/knowledge?

I ask because I have worked in each sector, and in my search, I'm not targeting one sector or the other, but now wondering whether I need to narrow my search. Maybe it's an industry specific question.