Take a look for yourself: http://www.seeing-stars.com/Buried2/
The answer is no, for the most part.
The kind of markers/headstones on stars' graves range from the very simple (such as Jimmy Stewart's: http://www.seeing-stars.com/ImagePages/JimmyStewartGravePhoto.shtml ) to rather large sarcophagus (such as Betty Davis': http://www.seeing-stars.com/ImagePages/BetteDavisGravePhoto.shtml ).
The only really elaborate one that comes to mind is the grave of actor Douglas Fairbanks. It is huge, and includes a reflecting pool: http://www.seeing-stars.com/ImagePages/DouglasFairbanksGravePhoto3.shtml