It's not clear why Obama had not previously divulged Rezko's tour of the house with him. In 2006, he told the Tribune he recalled talking to Rezko and his wife "either at an event or some conversation we had where they mentioned to me that they either knew the property or knew the developer or something like that.
Both John Ruberry and Steve Rhodes believe Barack is hiding part of the story.
I think what's being hidden is that Obama and Rezko had an arrangement, probably verbal, where Rezko would buy the side lot and agree not to develop it until the Obamas could afford to buy it back. In other words, a loan or a gift, depending on what the agreement was. Barack would not want to reveal this arrangement, which explains his vague answers on his discussions with Rezko prior to the purchases.