Why do both the 32-bit and 64-bit Visual C++ redistributables need to be installed on a 64-bit machine?

This article applies to:
7.x Briefcase for Windows, Email Manager for Outlook
6.x Briefcase for Windows, Contributor Pro, Email Manager for Outlook

If you are running Windows 7 64-bit, both the 32-bit and the 64-bit Visual C++ 2010 Redistributables are installed. This is because our program is 32-bit, which runs inside the Wow6432Node on a 64-bit machine. Therefore, we require both bit depths of Visual C++ 2010 Redistributables to be installed.