....I struck out ComputerGenie's comment - it's complete nonsense.
It was an attempt at a joke that apparently only I found funny. 
The coinbase transaction must exist in all blocks, even empty blocks.
The coinbase transaction is what sends the 12.5BTC + txn fees to wherever it goes, in our case 99.1% to the pool balance and 0.9% to an address that I decide what happens with (usually to me, but as in December, ~3.1 BTC went back to the miners)
His question was with regards to other transactions in the block, which was indeed less than most of the blocks we find.