Well, there are many token models out there. I guess that Vitalik and Joseph had the pure staking token model in mind: Tokens are primarily used to for staking in the plasma chain. And the fees in the plasma chain are also distributed only to the people, who are staking - maybe by a block reward.
Then the usual people using the plasma-dapp would just pay some fee in eth and they would not lose anything if the data-unavailability occurs.
Be aware that there are also solutions which motivate operators to ensure data-availability, even when they are bonded by Ether only. With snarks/starks one is able to do decide on data-unavailability more objectively, for more info see here.