The stated monetization strategy for the Ripple system is to hold some XRP and hope they increase in value. The optimal execution of this strategy is to balance the opposing goals of wide adoption versus XRP price maintenance. It is against their economic best interests to price transactions too high.
Yes, quite right. And that monetization strategy is where this whole project is rotten. Even so, if they manage to keep a balanced transaction cost it may well succeed (~ make the founders extremely rich).
The easiest way to stabilize transaction cost is to use the hoard of XRP to fix the price relative to another currency (e.g. Bitcoin).
Keeping a currency's exchange rate fixed is not cheap, and considering that they're starting out with a hoard of XRP that's not worth much (for a currency), it would be hard to keep it up. Well, it depends on how quickly XRP are destroyed and bound to new accounts. Perhaps they could keep it up for a while.