This is incorrect, or at the very least, rather ambiguous. The blocked seats look like any other chosen seat on the plane. Gray with an "X" through it. The only difference is that if you scroll over it with your mouse, no seat number will pop up like with the other seats. The way to tell if a 738 has blocked middle seats, one has to go no further than checking if the front row is row 8 (yes), or row 7 (no).