True, but, OpenCoin interest is aligned with all XRP holders. And the ripple market is also much more transparent than conventional markets. Anyone can watch the OpenCoin addresses (like we can watch Satoshi addresses). And everyone can see the amount of funds entering and leaving gateways. Compare this to the current bitcoin exchanges, where whales and exchange insiders have an exclusive knowledge of fund flows, and therefore a huge information edge.
There is no way to prove that OpenCoin isn't "giving away" the majority of their XRP to addresses which actually are controlled by OpenCoin (or their employees) themselves. They would have to reveal the identities of the users behind those addresses for that, which is not going to happen as it would compromise the privacy of these users.