Because Exchange 2007 is completely based on Powershell, which means that every change made through the Exchange Management Console or through the management shell can be logged.
Damien explains which keys you have to change in order to log the commands:
For the Exchange snap-in we will have to set the following regsitry key:
set-itemproperty HKLM:\SOFTWARE\Microsoft\PowerShell\1\PowerShellSnapIns\Microsoft.Exchange.Management.Msh.Admin -Name LogpipelineExecutionDetails -value 1
HKLM\SOFTWARE\Microsoft\PowerShell\1\PowerShellSnapIns\Microsoft.Exchange.Management.Msh.Admin LogpipelineExecutionDetails 1
From now on all commands executed by the Exchange management console will be stored into the event viewer of the server which could be monitored by Operations Manager (MOM)