RUNE is the base asset pair for all pools, so a 1:1 ratio of RUNE:ASSET is required for staking. A pool with $100,000 in BTC will require $100,000 worth of RUNE. In addition, in order to provide network security, THORChain requires twice as many RUNE to be bonded by network operators as there is RUNE staked. This 2:1 bond:stake ratio, combined with the 1:1 pool stake ratio, means that the amount of RUNE needed in the network is three times the amount of the non-RUNE assets locked. If $1,000,000 worth of tokens are staked in THORChain, the market cap of RUNE will be at least $3,000,000. And like any token, stock, or asset in the world of finance, speculation around future value encourages additional upward price pressure. The 3:1 ratio is just the minimum value of RUNE.