As you are probably aware resolution and device independence is one of the fundamental design goals of WPF. In order to achieve the desired effect the framework does not work directly with physical (device-dependent) pixels but abstracts this notion into device-independent measuring units like inches.
There are two main benefits that you get from this:
- Automatic DPI-aware scaling
- Sub-pixel positioning -- WPF coordinates use floating point numbers that theoretically give you the ability to draw with higher precision than the one provided by the ordinary pixel grid.
However, there is one nasty side-effect related to the fact that WPF graphics are anti-aliased by default...