I don't know how to explain this other than they are only looking for an alive Caylee. This is why LP put up the $50K reward for awhile to entice someone to lead them to the body, but he has since withdrawn it. That being said, all reports are that the reward is only for bringing Caylee home alive. I will check into it later when I can or someone else can help find this information for you. (I think we have GA stating it on a video.)
We don't have to believe this man or know his motives for what he is doing at the moment. Since it was never released where the woman thinks she saw Casey coming out of the woods and her car...it only makes sense this sighting needs to be checked out. I believe that when the driver sent Blink the pm with much of the same information a long time ago, it adds a bit of credibility to this man's story.
LE has gotten thousands of calls from people, probably some from WSers, with wild theories, speculation, and other tales. Do I find it impossible this lead wasn't checked out or somehow fell through the cracks? No. It is quite possible with the volume they have had to systematically go through to get to the ones that really matter. (This is exactly why I advise never sending LE tips unless you were there or know who was. Direct information!)
I am hopeful that if LE didn't take him seriously before or they missed his tip, they will be all over it today after seeing it on the news. They do need to hear him out. I would guess he would be willing to take a LDT to confirm he at least believes the story he is telling them.