That is no longer true in 8.1.
Yes, and to clarify: In Windows 8.1 including RT, merely swiping down leaves apps in a "sleep" state, but they're not actually completely closed. Windows users are used to simply closing any application, while iOS/Android users are not (you'd have to go to the apps list in either of those OSes to actually stop a running app).
To properly close an app in 8.1, you must swipe down and
hold for about 3 seconds until the tile icon flips around. Or you can use alt-F4 on the keyboard, which is faster, but currently I know of no method to make the flippy-time faster.
I wish MS would make it an option, really.