No we can't assume it will happen every time, but so far with Mr Duncan, Ms Pham and Ms Vinson, all we know previously about the virus has been borne out - that its not easy to get at the early stages (though not impossible) and very easy to get at the later stages.
I do not think we will see an outbreak due to the NYC doctor. But that doesn't keep me from lamenting the fact that he showed poor judgement. The chances are very low of transmission in early stages, but not zero. He didn't need to hop on the subway and go bowling. I mean, have some consideration for others. Again, chances might be low, but he knew his own travel and situational history. He had been treating Ebola patients. If anyone should have self-quarantined, it should have been him. I feel fairly safe in saying that IMO, he acted like a complete dumb-a$$. No common sense at all.