In OS X, is it better to put apps in /Applications or in ~/Applications?
What no-one seems to have pointed out so far is that /Applications are usable by everybody &amp; ~/Applications are only for that user.  

Some installers will ask if you want to install for this user or for everybody. That's how it can differentiate.

That will be one of the reasons Steam installs to there, as it's a per user license.

Apple's app licensing, though 'per ID' doesn't prevent all a machine's users from accessing apps purchased under another user account, so everything else usually goes in /Applications by default.

Of course, if you're the machine's sole user, the distinction becomes moot.