Skype for Windows 8 *not* Always On

I've noticed that if you Alt-F4 out of the app (or when you start up your PC, or if the app closes automatically after idling) that Skype sets your account to offline. Surely this defeats the purpose of Skype being always on, i.e. having the app open is just the same as having Skype on in the system tray in Windows 7. I was expecting it to be a bit like the Mail app, whereby the mail app can still recieve notifications even when i've alt-F4'd out of it, so why can't Skype?