They strategically remove/tone down shine (on the nose, forehead and chin, for example. Then they'd refresh the 'glow' on other areas where light would normally hit (mostly the tops of the cheek bones). For example, see JLo's Waiting For Tonight video at 1:04 and 1:31: Jennifer Lopez - Waiting For Tonight - YouTube
. Although she's pretty shiny all over her face.
As for Nicole Kidman, do you mean this pic?:
Her MUA powdered her nose and probably forgot to wipe away the excess. Powder is also applied under the eyes before eye makeup is applied to catch the "fallout" (the eyeshadow dust that falls onto your cheeks) and the MUA forgot to wipe that away too. The reason I say s/he "probably" forgot to wipe away the powder is because the MUA instead might've used a powder that flashes back (looks white) when photographed. Just looking at NK's face under normal lighting, you wouldn't see the whiteness.
I do that a lot. If you don't have the kind of curl you want, you create it. And sometimes that requires straightening to start from scratch, so to speak. And you know how beauty trends change. Something that was so faux pas yesterday is today's must-have look.