I think a significant part of the obesity epidemic is acceptance of being overweight as "the new normal". Certainly, we need to love our overweight friends and relatives for who they are, but I feel we should still do all we can to encourage them to lose weight.
Celebrities can do much to promote a healthier lifestyle, just because of their visibilty. From Oprah to Kirstie, we see them do the same things the rest of us mortals do. And do not forget the opposite end of the spectrum: the anorectics.
We just have to come to terms with the fact that there are health consequences to being overweight and deal with it, no matter what the actresses are doing.