I'm thinking Pearl Izumi seems to run exceptionally small. I'm generally a small in pretty much anything of a SML system, but I bought one of their jerseys on ebay and it seemed really tiny. Not sure if it's the brand or if I just got an odd style.
Overall, I would agree that Pearl Izumi jerseys tends to run abit small. I am small or extra-small myself. Without the jersey being tight on me. (I can't stand tight jerseys while cycling.)

I don't see anything wrong that certain manfacturer's lines run small or larger or whatever. We're all different sizes and shapes.

There is a potentially large market of women (for cycling wear) who would fall into my size category..outside of North America. But for current sales, it's interesting....maybe Pearl Izumi has a great market niche somewhere in the world that we don't quite know which there are women who would be buying smaller/tighter fit.