because they have an odd angle on the plate and it would be hard to call a ball inside/outside. The ump is standing right over the top of teh plate. MUCH better view. But the 1st and 3rd have a much better view on swings. That's why they are referred to for check swings... They alos have a better angle one a borderline pitch when a catcher pulls a ball into the strike zone. . Like TT said, no they dont. They are at an angle, which makes the edges of the plate and borderline pitches harder to determine.