If someone wants to start a website and integrate steem (or any SMT), while making it frictionless, he'll want to put all the blockchain stuff in the background. So users will come and sign up like on any other website, even without buying steem. For that to work, the website owner has to delegate RCs to the new users. Therefore he must hold Steem Power.

The more users a website has the more it will use the blockchain and the more it will need RCs, so again more Steem Power. If the website owner does not have enough Steem Power, he will either need to buy more or to lease RCs from other Steem hodlers.

If there is enough demand for dapps on the steem network then in the end RCs and Steem Power are going to become scarce. That is also without mentioning speculation and the fact that Steem Power increases your influence (through witness votes and the SPS).

For example, if a successful dapp wants to have a bigger say into who is a witness, or if she wants to fund a particular project through the SPS, the only way it can increase its vote value is to buy Steem Power.