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They are related. Every block, there are 21 'miners' that contribute to the 'Delegated Proof of Stake' calculations. Each of the top 19 witnesses, plus one backup witness (chosen at random based on a weighted probability of their vote shares), plus one miner.

Everyone in the non-witness mining pool is basically on equal footing, and it is largely a competition of computing resources. For the witnesses, the more votes they have, the more blocks they will get.

The top 19 witnesses also have additional responsibilities in that they set the parameters such as the price feed and SBD APR.