According to Apple's File System Overview…

Originally Posted By: Mac OS X File System Overview
Applications should be placed in the /Applications directory or the ~/Applications directory of the current user. Applications placed in the /Applications directory are available to all users on the system. Applications placed in a user’s home directory are available only to that user.

All of the resources and data files required for an application to run should reside inside the application bundle. However, applications often come with extra files, such as templates, plug-ins, and other application extensions over which the user has some degree of control, including whether or not they should be installed. Similarly, an application might generate cache and temporary files that should not reside in the application bundle.

The remaining sections include some of the appropriate and inappropriate locations for application files. For information about the purpose and intended content of specific Library subdirectories, see “The Library Directory.”

The Mac App Store is therefore enforcing compliance with Apple's own developer standards by defaulting to the /Applications folder. To do otherwise would make the developer standards meaningless.

For those who want to move MAS purchased apps to another folder you can do so but with two caveats:
  1. You will be required to enter an administrative password to move the app from the /Applications folder.
  2. If an update appears in the MAS for an installed app that has been moved you will get an error message about having apps installed from another account. To update the app you will have to
    1. Delete the app entirely and then install the updated app or
    2. Move the app back to the /Applications folder

I learned all of this the hard way.


"All you've got to do is own up to your ignorance
honestly, and you'll find people who are eager to
fill your head with information"
--Walt Disney