First, your question about why placemarks don't have ships under them. The placemarks in this thread date back several years, and the image database that Google Earth uses has been updated with newer imagery many times since they were first posted. This means that movable objects that were once visible may now have moved and aren't visible anymore.
As to your comments about the USS Arizona, if you look in the lower left corner of Google Earth, you'll find the "Layers" menu. The second item on the list is the "Keyhole Community BBS", which contains placemarks for many of the posts made to the BBS in the past. If you turn this on, you'll find that the USS Arizona is a popular spot.