Why must all areas connect to Area 0?

From: CCIEin2006 (ciscocciein2006@gmail.com)
Date: Mon Oct 29 2007 - 10:12:10 ART

Hi folks,

I was reading over Jeff Doyle's blog and came across his favorite interview
question:
Why does OSPF require all traffic between non-backbone areas to pass through
a backbone area (area 0)?

Answer:
Because inter-area OSPF is distance vector, it is vulnerable to routing
loops. It avoids loops by mandating a loop-free inter-area topology, in
which traffic from one area can only reach another area through area 0.

Can someone elaborate on that answer a little bit? Exactly how does having a
connection to Area0 prevent routing loops? Is it similar to spanning tree in
the area 0 is the root of the spanning tree?

Also this answer does not take into consideration redistribution from
another routing protocol right?

Thank You

Here is the article:
http://www.networkworld.com/community/node/19293

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