People think the banking deals settled by Ripple the company are similar to banks positioning themselves in XRP the token, but that's not the case. XRP is nothing more than a product without any purpose other than allowing people to move value quickly through its centralized ecosystem. If people like using centralized garbage they can just as easily keep using PayPal, and the best thing of all is that PayPal has no insane premine. 
Exactly that is why I think it's concept doesn't make much sense. If you have no problem with centralization, a client-server architecture is usually cheaper and more efficient than a blockchain.Quote
Ripple the company, or more precisely said, Brad Garlinghouse and his buddies, own 60% of all the XRP tokens in existence already (they are currently locked up).
You're right, that may actually be the main reason for the "apparent stability" of the XRP rank.However, as banks (and other users) using the Ripple infrastructure occasionally have to deposit funds in the Ripple ecosystem (and take certain exchange rate risks) when moving funds through it, and even have that may also be a major factor driving up - or at least, stabilizing - its price. Remember that most altcoins also have high premines (up to 100%) held, at best, by a group of whales, but they don't have the ecosystem Ripple can count with.
By the way, I think we could get a better measure for a coin's "popularity" or "value" than "market cap" if we try to measure its transaction activity. Probably Bitcoin's "dominance" would be much higher. Coinfairvalue tries something like that, but has some pretty strange valuations ...