My general understanding is that, while they use the same equipment (needle and thread), sewing and crafts like embroidery are not the same.
I recently submitted a tag wiki excerpt for sewing that states this specifically and encourages users to use the craft specific tags for embroidery and cross stitch rather than using the sewing tag.
It seems that sewing generally requires that you are attaching two things to each other and the stitching itself is generally hidden as the product is the art work, not the stitching.
Embroidery is all about the stitching and nothing is being attached (other than possibly small accents like jewels).
This is not to say that there will never be an overlap... many embroidered projects end up sewn into larger pieces, as in quilts.
But, in general, should we make sewing exclusive of other needle crafts?