Windows 10 users will be able to run the OS on PCs, tablets, smartphones and even on some non-traditional platforms such as gaming consoles and wearable devices. But only universal apps are compatible across all Windows 10 devices.
Universal apps allow an application to run on any Windows 10 platform, regardless of the device type, but the app might not appear completely identical on all platforms.
The application code of universal apps formats the application’s display based on screen resolution. As such, a low-resolution device such as a smartphone might display the application differently than a higher resolution device would. But if you shrink the size of the application window on a high-resolution device, the application will reformat itself and take on the same appearance as it would on a lower resolution device.
It appears that the Windows 10 interface will be mostly consistent across device types, and the universal apps will also be consistent from one device type to another (aside from the screen resolution issue).
The Windows 10 Desktop Mode is not available on all device types, however. Only PCs and some tablets support Desktop Mode; Windows Phone, Xbox One and certain tablets do not have Desktop Mode. This means that it's not possible to run a desktop application on every Windows 10 device.