it's probably self-imposed, but honestly, i'd probably be very concerned about my weight, hair, face, etc. if i had that kind of scrutiny 24/7. it has to be terrible, in that respect, being in the spotlight like that. everyone sees your pores, etc.! consequently why some are a bit too thin: kate, letizia, mary.
I haven't been following Charlene at all, but I think Kate became more focused on her weight right after the engagement, and it was very unfortunate. Did it come from William? From her mother? From someone else? Or her? If she truly is concerned about how she looks in high definition photographs, she should employ a makeup artist - and a stylist. She'd look much better, if she did. She doesn't need to look skeletal - it's all about proper tailoring, good makeup, and nice hair styles. But ultimately though, it would be especially refreshing for her to just start working and forget this whole 'runway' nonsense. If she had a work ethic, she wouldn't need to focus so much on her d@mned appearance.