I fail to see how "Witnesses power the blockchain".

Or is this due to your other comment in regards to the common misconception that witnesses were the ones running the IPFS nodes and not just the average everyday joe blow with no power at all?

Yes, it's due to my misconception. I thought they had a similar task as the Bitcoin miners. I had that misconception, because of the following sentence in the Steemit FAQ:

The remainder is distributed to holders of STEEM Power and the witnesses that power the blockchain.