Sheesh, everyone into conspiracy theories..
No, there is a very good, clear reason for this. In fact, if you search a bit harder on the Hubblesite they will explain it for you.
Basically the camera is made up of three big CCD chips and one smaller one. The smaller one actually has a higher megapxel count and is used to specialty work. But for larger areas when they put the put the four together and you get that zigzag down one side.
Simple answer. Occam's Razor. Don't make answers any harder than they have to be and ditch the conspiracy theories, huh?