UEFA (FIFA?) regs state the max distances allowed for football viewing from one corner flag to the opposite end of the stadium is 190m. Here's how that looks for the olympic stadium, and why the seats in black (blue on this pic) are not in use
http://img.prntscr.com/img?url=http://i.imgur.com/YFPu5J2.png
I actually think when West Ham increased the capacity to 60,000, they just put those seats into use and are selling them for cheaper (I may be wrong).