Where exactly do they say they chose the most iconic covers? Britney, Christina, Justin, Jennifer Aniston etc. had much more impact than Gaga's forgotten one.
Gaga is the only artist to debut post-2000 to make the cover list. Truly the most iconic artist of this millennium with her cover alongside countless other industry legends.
Out of all the ones on the cover and all the ones mentioned in this thread I've only seen the John/Yoko, Britney, Janet and Jennifer Aniston ones before.