Interested in knowing why?

First off, I am not sure if this is the right forum for this type of question. Secondly, this is a "technical" question whereby I am not sure why this was done.

So here are the questions:

I was reading up on grenades last night (don't laugh, it's a hobby) and in the section dealing with the M26 (lemon) series of grenades it showed a diagram of an M26. In this diagram it showed the explosive as Comp(osition) B and surrounding the detonator were small blocks of Tetryl. On the rest of the M26(A1-A4) diagrams the explosive was the same but there were no Tetryl blocks surrounding the detonator. Now I believe that Tetryl is considered a booster charge for other hard to detonate explosives. My question is therefore, why would they drop the booster charge on the rest of the series when the fragmentation radius remains the same and the amount of Comp B increases by an ounce or less on the A1's and above and why would it intially have one in it in the first place. Also, is Comp B one of those hard to detonate explosives?