What is the logic to having an axis labeled Z and also having Z refer to distance from the camera? What is the logic to having an axis labeled Z and also having Z refer to distance from the camera? It seems like an easy way to confuse people. Is this due to the conjunction of two different lexicons, one from geometry where they have a Z axis and one from photography?
Quoting from iKlsR's answer:


  Blender uses the right hand coordinate system with the Z axis pointing
  upwards. This is common with the coordinate systems used by most
  common 3D CAD packages.


However, it's also a standard to use Y up for images (with Z as depth).

To help with getting used to it, you could try a couple things:


Imagine you are looking at the image editor top down instead of from the side.
Think in terms of the camera's local coordinates (the local Z is always out the front)