RPP tackled the same question (why 2 and 4-seam fastballs are different) back in July and came to the same conclusion (that seam orientation in itself does nothing) but from the opposite direction. They showed that a 4-seam pitch with side-spin induced at release would run the same way as a 2-seam. Have a look.
Bahram tells me they used Wilson 1010 balls. Our study used very similar 1030 balls. Each of these have a high seam.