I believe with UAC on you can install to Program Files but if you try to create a text file under Program Files you will find that you cannot. Furthermore if you create a Word document and try to save it to c:\program Files, an error is generated at least that is how my system works.
The default setting for UAC does not permit writing to the tree under "Program Files". Instead Win7 creates a shadow folder under the current user where new/modified files are saved. For example when your app says it is saving to C:\Program Files\ it is actually saving to...