In the Perspective Window, the mouse buttons correspond to the world space coordinates (X,Y,Z) to allow free movement in all axes. When moving, the left button constrains to X, middle to Y, and right to Z. For rotation, the buttons rotate around each axis; and the scale tool scales your objects uniformly.
The Perspective Window can be used exclusively in a one window workflow. Select any of the ViewCube's 26 preset views (faces, corners and edges). These presets behave like the orthographic windows and thus have the same move constraints using the middle and right mouse button.