stat.mineBlock will only increase if a block is broken in survival or adventure mode. Because command blocks can only be destroyed in creative mode, stat.mineBlock.minecraft.command_block can never be increased, rendering it useless.

Blocks that can only be destroyed in Creative mode should allow stat.mineBlock to track breaking in Creative mode, or the statistic should be removed to prevent confusion (although Creative mode tracking would be much preferred for these types of blocks).