There are 36 total 4-patch units. If you were to divide the 36 by 4 rows equally, you would have 9 in each of the rows. However, since there are four corner patches that need to go onto each corner, you will put one on each end of two rows. That will leave only eight in each of the two remaining rows.
If you look in the center box on page 6 you will see where Sue explains this.
Please correct me if I'm wrong, but I think there's an error in the instructions regarding the number of four-patches needed for each of the four borders. :
Page 7 (at the top) says: "lay out the four-patch square into four lines; two should have ten four-patch units and two should have eight 4-patch units." However, I think that's wrong. They should all have eight 4-patch units initially. Two strips will become ten 4-patch units when the two "odd" four-patch units are added to each.