Also HBase (http://hadoop.apache.org/hbase/), which has some nice features like replication, compression, recovery from node failure, and integration with Hadoop.
Another point is that with a b-tree you have your rows in sorted order, which means you can do "select * from blah where id > 100 and id < 200" and you're still using the index. If you were using a hash table, you'd be doing 100 random disk seeks instead of a few sequential ones.
Wow. I understand that fits really nicely in your world model that unifies economics and morality, but that's not how the world works at all.
Borrowers are not always rational or informed. Most people go into debt because they spend beyond their means, not because they're leveraging short term capital. Payday lending is illegal in some states and a felony in Georgia. This guy made $70 million off poor people, pushing a large number of them further into debt, and you're calling that the measurement of his goodness?