IMO, Caylee's remains are the biggest piece of evidence that links Casey Anthony to the Suburban site. Like others have pointed out, it all ties together.
Casey was the last one on the face of this earth to be seen with an alive Caylee. The person that Casey claims to be the last person to be seen with Caylee doesn't even exist.
Casey's car has evidence that a decomposing body was inside it. Her own parents made comments that the car smelled like a dead body. LE said it smelled like a dead body. The towyard guy said it smelled like a car where a man had commited suicide. The biggest piece of evidence, IMO, that confirms that a dead Caylee was in that trunk is the piece of hair with the death-band that matches Caylee.
When Caylee's remains were found there were things that could have only come from the Anthony's home. You have the duct tape. The Winnie the Pooh blanket. The little pair of shorts that do not match what Caylee was wearing when she George said they left the house on June 16th.
Okay, so Casey says that Zenaida had a key to the house? The jury is going to know for fact that a nanny by the name of Zenaida Fernandez Gonzales does not even exist by the time they get to this little gem of information.
Casey's phone pings, her text messages, the lies she told, the computer searches, the phone calls home from jail, the jail visits, her letters are all just icing on the cake. Not to mention all the people who did have access to her when she was out on bond and she never spoke of Caylee.