I don't think there's anything wrong with what MrThaibox (the creator of this apparently controversial video) is pointing out. And yes, everyone, this version of Mac OS X is a Developer Preview. Plenty of time for developers and users to go to apple.com/feedback/ and give Apple the communication they need to make this OS release work better for everyone.
There could be the following settings in System Preferences:
Desktop and Screensaver
✔ Desktop Background spans all displays
Displays
✔ Application windows can use multiple monitors
We need to look at this video for what it is. Info to the masses and feedback for Apple. A Mac should be able flex to the user's needs. OS makers (i.e. Apple) can only see all use cases when they let a large user base test it.
Perhaps MrThaibox uses multiple monitors because it makes him more efficient at making a living. And what if a production studio uses this setup? I'm in no financial position to even buy ONE new monitor, but just because he made that investment in his workflow is no reason to start bashing him.