the matrix of the infinite far plane

example of the infinite far plane perspective matrix is

   |   2*Near/(Right-Left) , 0, (Right+left)/(Right-Left),0 
   |    *                 , *,        *           ,*         
   |    *                 , *,        *           ,*     
   |     *                 , *,        *           ,*

My question is why not write 0 instead of (Right+left)/(Right-Left)? Is the equation of Right=-Left is not always right in the perstective projection? The same happens to (Top+bottom)/(Top-bottom), Top should be equals to -bottom?

Indeed when you have an off-axis projection, like typically used for stereo rendering, right is not equal to -left.