Creeper explosions not refunding all blocks

Out of the 10 explosions for both for Creepers and TNT of crude testing;

Creeper on the left. When a creeper explodes, not all the item drops are there (number next to craters are blocks missing). An average of 27 blocks missing per crater.

TNT on the right. TNT dropped all their blocks except for one circumstance where it lost 1 block.