Inquiring minds have discovered that for some reason the Windows Installer service goes on for about 10 minutes and asked 'what that heck?'.
Yes, it is by design that the Windows Installer service will remain running after the install. If there are no installations for 10 minutes, the service will automatically shut itself down. There is no way to disable that behavior, although as with most services, you can try to stop it by sending a stop command.
Note: Content from Carolyn, MSI Team Dev Lead. You can get other Carolyn insights about developing for Windows Installer from the Windows Installer Chat Archives