i agree that the spikes (in astronomy images) don't come from blade edges in a diaphragm aperture, but they are still diffraction spikes (from the secondary support) and "everyone" (as far as i know / remember) refers to them as such.
you can see the secondary support in the top right image at http://en.wikipedia.org/wiki/Reflecting_telescope - the four radial "things" that hold the cylinder in the "end" of the telescope (on the right).
so what are you referring to with "internal back reflections" and how does that give spikes (rather than ghosts)?
[above from (past) personal experience as an optical astronomer on research telescopes - i am not sure if you are confused, or if there's some kind of problem i never understood. perhaps you work on a system where this is an issue?]