(In my case what I suspect is mistakenly someone has deleted this IUSR user account from the CCM incoming Virtual Directory.) So the HW inventory data in the server is not in sync with the delta reports which client is sending, hence the server will issue an inventory resync request to the client.
In case if you come across with the issue where the Config Mgr 2012 SP1 is not gathering the Hardware and software Inventory, following is one incident which I faced.
Software Inventory Rule information (what an administrator has configured SCCM to inventory) is stored within the same namespace of WMI (Root\CCM\Policy\Machine) Each rule is stored in an instance of this class.
Once the properties of the scan have been determined, and the Advanced Client knows what type of scan (Full, Delta or Resync) to perform, as well as what it is scanning for (as defined in the Software Inventory Rules), it is time for it to perform the actual scan.
Once the Software Inventory Client Agent has determined its Scan type, it must now determine precisely what it needs to inventory.
This is accomplished by again pulling configuration data from WMI.