As a photographer myself I can tell you - yes they do not seem as the same person - especially when your face features are almost simetrical - because any kind of light can modify your look , also to mention the different focal lengths of the lenses used. From a wide to a tele lens, your face can get more chubby or more narrow. So yeh this is from my point of view as it falls into my area of expertise. Also her appeareances especially in MCE and Gourmandises era were spaced in a time where she developed as a human being so hormonal changes and stuff can really change your face appearance aswell as body. But it's a guess...
Other than that : "The girl next door" ideea... Not something we here use so I think it's most of the US that are familliar with the phrase but : In essence it reffers to something familiar that you adhere to . I do not know why we are drawn to these features - she is incredibly beautiful but not the only one out there for sure. Yet you do not feel the same attraction to the rest of them but only a few - and most seem to share the same features. Maybe because you feel she is not as unreachable as you think despite her fame and status. Her attitude makes you think that - maybe that's why a lot of people actually fall in love with her.
But there must be more to this - I mean the fact that I listen to her music and it uplifts me in certain bad times in my life is strange - especially when I do not like this kind of music anyway - I am way too far in genres of the music I like to actually be a fan of her songs - yet I am - I do not have to watch her perform in a video - I can just listen to the song itself. Maybe I am just weird
Also as someone stated in the thread - no matter if she changes looks , style , attitude etc. you get the same feeling. And of course changing from the extrem introvert to the extreme extrovert styles in just moments makes it very attractive. You see this absolute amazing human being perform and see her as a godess because of her dance , attitude etc. and then she steps down and has this shy , modest , kind of like she doesn't know why she's there - attitude and you are mind boggled. It's like a Dr.Banner to TheHulk transformation - metaforically speaking