I realize that the almost-goal will be a sore spot for many fans, so I've broken it down for convenience.
Note the ACTUAL SIZE of the ball here. Click on the picture to enlarge for an even better look.:
Now, note how much of the ball you can see here. Again, click on the picture to enlarge:
Now, does THAT look like the ENTIRE ball is over the line? Obviously not. The definition of a goal is that the entire ball has to be over the line. Even though the camera is slightly off, the angle it caught the ball from actually makes the ball seem smaller than it really is by filling out the rest of the shape with the white frame of the crossbar.
I rest my case.