SSIS package deployment does SOMETHING

Everything I read out there says that SSIS package deployment to file system does nothing more than a file copy.

I created some SSIS packages and called them from an asp.net site on the same box. However the asp.net site couldn't find the packages until I deployed them to the file system.

So deployment does something, either to the permissions of the deployed packages or by registering them as available somehow. Is there a hidden GAC equivalent for packages (GPC??)