I suppose it could be the fact that she always had a fairly well defined path she wanted to take and she took it, and made it quite clear she was only doing the "celeb game" for her own financial benefit and not as a career choice. I suspect people wouldn't be so positive about her if she was still doing the glamour work and still selling the 'sex kitten' image.
For me, even when doing the sexy stuff, she always seemed to be a bright, decent, pleasant girl. I might be wrong but I don't remember her having digs at other women, slagging off people and generally attention seeking.
It's like Kelly Brook really. It's not the job that people criticise, it's the person and how they conduct themselves