I think petites are cut differently too. I can't wear a petite size 4 in a lot of placesbecause the waist doesn't come close to reaching my natural waist and a 6 is too baggy in the butt and thigh area.
I'm about 5'5 about 117 and wear a 4 in places like gap, express, limited. My legs are short however, and often pants are cut so wrong for my body type i have to go a size up...and it ends up looking awkward. My biggest problem is my waist to hip ratio. I have a very high waist, at the narrowest point about 26" but my hips are a tee tiny 32". It's so hard tha I try to wear size 5 hip huggers from the juniors departmens and they fit fine, but slide right off after an hour of so of wear, because I have nothing to hold them up.
I think I look bigger than I am because of my awkward body shape.
Em