Why would I buy an IOU from a third party when I can simply send ETH to the DAO address in order to get DAO tokens straight from the source?
Because you are able to trade the IOU immediately. So in the last days when DAO will cost more eth you will have a profit.
For those who don't understand what is going on, here is the incentive:
* They bought DAO in the first 14 days for the maximum bonus (2 days remaining to buy at this rate).
As the price continues for the next 10 days after that, it is a linear increase in price. For the final 4 days, it is 100 DAO for 1.5 ETH. Right now, DAO being available on openledger is pointless as you can buy directly from the source, easier and safer. However, in 2 days from now up until May 30th, they can undercut the current price because they bought their DAO for the cheapest rate.
The final 4 days when DAO price gives 33% less tokens, Openledger market could undercut by up to that much and be a better deal for late buyers, and Openledger can offload their 50 btc worth of ether for 1-32% profit.
https://bitcointalk.org/index.php?topic=1470496.0