Ancient Rituals: Many Cultures Seem To Have Similar Ways Of Doing Them

I've been boning up on information about or related to Peru since this summer.  The other day I got a book out of the library about the Incas.  While I was reading it, I came across a passage that talked about the sacrifices performed when a new ruler, or Sapa Inca, was crowned: Two hundred youths would be sacrificed and then buried with specific items (the book did not say precisely what, unfortunately).
I found that to be quite similar to the Shang Chinese royal burials.  When the king died, hundreds of prisoners and slaves would be beheaded and buried with him in the tomb.

These two cultures were thousands of years and one ocean apart.  But there's something about those two rituals that makes me ask a couple of questions:
1) How common was this kind of ritual in the ancient world?

2) Why was it done?

The trouble is that I haven't read much about either the Incas or the Shang in a long time so I'm very rusty on their history and just beginning to learn some more about them.  For years the only things I remembered about the Incas were their sacrifices (National Geographic has several really good articles about those), Macchu Picchu, and the Conquistadores.  And all I remember about the Shang were their sacrifices and the bronze making.  So, I've got a lot to read about them still.  Heck, the last time I read about Macchu Picchu before this summer was back when I was twelve and my mom got a book about it out of the library. 
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Extra: I noticed that the same principle applies to art as well.  That is, I noticed that some of the jewelry found in the tombs of the various native Peruvian cultures is similar to the ones belonging to the ancient Egyptians.  Not that I think that they are related; however, I do like noticing things that look similar.