Yes, my shoulders are broadish... I think... I am an hourlgass that trends towards inverted triangle. I'm not sure if it's my shoulders, so much as my upper arms and the fact I'm a little ... rounded and soft and squishy on top (which is where I gain weight first).
But I don't have much problem with XS regulars in the shoulder area - at least when it comes to coats and jackets and blazers. I do often have issues with dresses and tops - depends on the style (for example sundresses designed for pretty pears - forget it!). I think coats and jackets tend to be cut a bit more generously, to go over tops. And that extra bit is all I need.
Then again, it's true that when trying on *petite* coats and jackets, I often go back and forth between the XS and the S or the 0 and the 2... either will work, but there is a difference in fit (see Tanya's recent thread, with her white jacket she just bought and she fretted about the size... it fits her fine, it's just a different look).
If it's a leather jacket, I definetly size down because leather does stretch over time. Jackets in general tend to stretch, because you don't wash them as often as you do tops, so usually I talk myself into the smaller size - unless it absolutely doesn't fit over my chest!!! (which is another issue). Or unless I want to wear it over jackets, in which case, I shop wearing a jacket, so I know it will fit over.
Does that make sense? Late here... I've been working non-stop all day on a project that was due, and now I'm vegging with a glass of wine and YLF and trying to unwind!