Why did Google copy off of Yahoo!?

In hopes of being short today on my thoughts about Google versus Yahoo! I think this whole copying thing is starting to get out of hand.

Long ago, Yahoo! made its own social bookmark/news service, called Yahoo! Buzz (2008). It is a lot like Digg, and has pretty good popularity.

However, Google very recently released their status update service called Google Buzz. Now, why did Google have to copy off of Yahoo!?

The difference between the two would probably be the privacy levels. Obviously they are two different services, so that is a no brainer there.

Now, it is unknown why this move was made by Google, but only time will tell of potential disputes between the two powerhouse search companies.