Mr_Faineant, are you sure, that the NEMA17 (upper link) is unipolar?
I'm not an expert, but I've been a little bit in stepper topics the past month and I once read, that the NEMA17 is a bipolar stepper motor.
I'm also not sure, if NEMA17 is a standard, so every NEMA17 motor is bipolar. But I guess, it is.
So I rather would say, that the upper link is a bipolar motor.
EDIT:
Alright, I just did some little research and it seems to be unipolar/bipolar.
Here the source: http://www.watterott.com/de/Schrittmotor-Unipolar/Bipolar-200-Steps/Rev-42x48mm-40V-1200mA-NEMA-17
(the description is in english)