In the standalone distribution of Confluence, the Modification section of the System Information screen is always empty. Like this:

The following error is given in the logs:

2010-10-05 12:34:57,806 ERROR [http-9090-4] [confluence.status.service.DefaultSystemInformationService] getModifications No registry provided.

This is because the hash-registry.properties file is missing from those distributions.

Note that if modification detection is working in Confluence 3.3 and no files are modified, then the modification lists will not be empty. It will expressly say that no files are modified, like this: