Although still obviously an early build, the version leaked showed that Microsoft is acknowledging that despite its tablet aspirations, Windows 8.1 is being used by traditionalists with a keyboard and mouse.
For example, running Metro applications are shown in the Desktop taskbar, like regular PC apps. Metro apps also get a title bar, like traditional Windows applications. Users can can minimize or snap them side-by-side with a mouse click from there.
Small improvements have been made to the Start Screen: Right-clicking on Live Tiles now brings up a menu with options to resize, pin, and more. Microsoft has also brought the search button and a shutdown option directly onto the Windows 8.1 Start Screen.
These changes show that Microsoft is still figuring out how to make its desktop OS work properly on mobile devices such as tablets, while retaining the ability to run optimally for desktop only users. Microsoft can't cater strictly to keyboard / mouse users, as doing so would kill Windows 8.1 on tablets.
However, legacy Windows users still want to use their Windows apps in a standard desktop manner, which is why Windows 8.1 -- which many said was what Windows 8 should have been out of the gate -- added features like boot to desktop and a (sort of) Start button.