Common within many communication type applications including instant messengers, email clients etc. (Lync, Skype, Spotify, for example), when I click the top cross (generally known to close an application), the application is actually minimised into my task-bar rather than closed, so that it is always available and I stay logged in.
This would be a smart move for the Lifesize Cloud, which would mean that the application would continue running in the background and the users would still appear for presence, and calls would still be able to be made. I believe this would also improve adoption as the application would be readily available and visible.
This isn't really an issue for Mac users where applications aren't closed directly by the cross, but for Window's users, it is.