Just looking her up on Google images I'm inclined to agree with you on her face. If you look up the older DVD covers with her from around 2005 she does seem to have less of an oval-shaped face and her eyes look smaller. I wouldn't put it past her to have had surgery to thin her face and/or widen her eyes.
I wouldn't say that so many celebrities do it because "most normal people in Japan are ugly." I would say that they do it because most normal people in Japan hold celebrities to a very specific (and unattainable) standard of idealized beauty. There is an ideal in Japan for women to have oval-shaped faces, wide eyes with double eyelids, narrow noses, and small lips. Many women who are attractive to begin with undergo surgery to change their face entirely just so that they can have these specific features simply because it is the current ideal. Junior Idols for example are usually forced into these surgeries by parents or managers even though their faces have not fully developed yet. It is really sad and objectifying to discover that many of these girls who were naturally beautiful to begin with felt the need to make such drastic changes to their appearance/identity in order to conform to one specific standard. =(