Why is Al Zarqawi so glum?

From Chrenkoff

Chrenkoff has an interesting take on the latest Zarqawi letter compared to the one in February and notes :

In both documents al Zarqawi claims credit for 25 suicide bombing operations - as if nothing more has happened in the time between the two letters.

It looks like al Zarqawi just keeps repeating himself four months on. And it's not like al Qaeda hasn't had a good run recently, considering all the hostage executions, suicide bombings and the fighting in Fallujah. So why the long face? What's really happening?
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