Why Unity compiled shader doesn't use the GLSLPROGRAM/GLSL syntax?

Quoting the Documentation

  "GLSL program snippets are written
  between GLSLPROGRAM and ENDGLSL
  keywords. "

, but strangely the compiled shader for the Android platform doesn't use GLSLPROGRAM/GLSL syntax, instead it uses something like this :

 Program "fp" { SubProgram "gles " {
 "!!GLES" }

or

 SubProgram "gles3 " {
 "!!GLES3#version 300 es
 }

1) Should I use this syntax instead of GLSLPROGRAM/GLSL?

2) why do we need the "!!GLES3#version 300 es" and "!!GLES" strings?