For the 920 the problem is that the glass is glued to the touch sensor (which might be glued to the LCD). So it isn't possible to just change the glass. At least of you want an 100% solution. I saw some YouTube videos about separating the glass using heat... Nothing _I_ would try at home...
So, if the glass is broken, a repair shop has to exchange the glass and the touch sensor. Official shops always exchange the full package, including the LCD.
This could be the case for the 930 as well.
My next phone will either have a separate changeable glass or insurance... Broke my 920 screen twice...