How do cemeteries work?

I thought you could put your dead sims in a cemetery grave and then visit and mourn etc., based on the trailer and information the Life & Death pack but I can't figure it out.  I had a very nice funeral at the cemetery that comes with and tried to put the urn/gravestone in a plot but it just sits there on top and you can mourn just like if you leave it on your counter at home but I thought it was more than that? The trailer said you could customize it and it looked like it would mark the plot as occupied.  

What am I missing?  No mods/cc