When a creeper explodes it always destroys all blocks in a 3x3 area around the creeper, none of these blocks ever get turned into entities. No additional damage to blocks outside of the 3x3 area seem to suffer any further damage from the explosion.

Since we can't use duping of TNT, i'm using creepers as renewable TNT. My farm has a mob farm above it, which extracts both creepers and skeletons and disposes of all other mobs. I drop the creeper into a 1wide, 2 deep hole surrounded by the block I would like to farm, either cobble/stone or trees. The skeleton tries to shoot a snow golem, but ends up shooting the creeper, the creeper detonates, and is supposed to turn 'some' of the blocks around the creeper into entity format, which are picked up by hoppers and stored into chests. However the creeper ALWAYS destroys all blocks around it, except obsidian, regardless to the blocks blast resistance. Furthermore the explosion does not seem to effect anything outside of the 3x3 area. I encased the area outside of the 3x3 with glass (very low blast resistance) and it does no damage to the glass at all.

Furthermore the creepers explosion damage does not seem effected by the difficulty. I expected to see a more powerful explosion which would have effected more blocks around the creeper, but this does not seem to be the case.