Is Desktop default mode for Kiosk?
I'm not exactly sure what you mean.
There are basically two "desktops" in the Kiosk. Tablet Mode and Classic Mode.
The default mode that the Kiosk starts in is tablet mode. Tablet mode is similar to the Windows 8 Metro-style GUI. It has app tiles that you can click on to open applications, like you would using a tablet.
If you're using Dragon and Silverlight, tablet mode is going to have some apps that your PC's desktop does not have. In other words, there are more icons in the Kiosk in tablet mode than are on your PC's desktop.
If you switch to classic mode, you will see only the icons that are on your desktop, and the layout is similar to what you are used to looking at on your PC's desktop.
If you choose not to install Dragon or Silverlight, accessing the Kiosk will only show the icons on your desktop in either mode, but it still defaults to tablet mode (albeit a stripped down tablet mode) when the Kiosk is started.