How did you reach that conclusion?
If Windows was Open Source, this would have been addressed a long time ago as this feature is desirable to what one would consider a power user. Advanced users are also the ones who roll up their sleeves and will fix a problem if they can, especially if no one from the parent company is making any effort to do so. But, thanks to Closed Source protectionism, they can't. And because their value to Microsoft is the same as any other user as they pay the same license fees as anyone else, the voice of the power user is drowned out and their concerns are never addressed.
This is just one glowing example of Closed Source working against the betterment of a platform.
Seriously, how can one NOT reach the same conclusion?
What exactly do you mean by that? I never had any issues with multiple monitor setups (or noticed any lack of features..)
I doubt that feature was approached with a "This better make up for the Ubuntu phone!" mindset.
Some features that may be lacking would be some Ultramon offers, like menu bar buttons to send the window to the another monitor or span the entire set of screens, but now that I run a 3-monitor set up with two in portrait mode, that sort of feature doesn't really strike my fancy. Plus dragging works.