I just did a fresh install of SQL Server 2012, all components (ex. DQS, MDS). During the installation, one of the dialog boxes asks about permissions. One of the options is to "Add the current user as an Administrator'. This is handy because it sets up the permissions required to then access the newly installed components. If you fail to assign anyone the Administrator rights, you may not have permission to then go and manage the components you just installed.
BUT, with Reporting Services installation and Setup, there is no option to assign Administator permissions to an account. The result is that once you have installed SSRS components, then used the Config tool to get it running, you don't have any rights on the virtual web directory to publish or otherwise manage it.
The current work-around is to open IE by right-clicking and selecting "Run As Administrator", then browsing to the Reports site and assign permissions manually.