I don't believe it is zero-sum.. Or at least, not rigourously. I feel the Market Capitalization of BTC must have been bootstrapped at some extent. It seems impossible to me that the sum total of what people have paid to have their BTCs to be more than $2.02T. In other words, the value the market gives it has given value to BTC out of nowhere.
Each transaction has a buyer and a seller. So in that sense it is a zero sum game. However the total market cap can go up and down and create value out of nothing (just like stocks).
