what is the difference between an aperture app and an aperture software

In my opinion, there is no current difference. Aperture can be installed from a box set (if there are any left) or from the Mac App Store. It may be the latter (which is cheaper too) that makes some people use the term App as an all-inclusive term meaning a download. App is short for application, which could be a synonym for program (countable nouns) while software (uncountable) has a wider meaning.

There are also many users who would welcome an app for the iPad or iPhone.

No problem. Hope it helped.

Not to belabor this, but I noticed that the price point difference is huge (about $120 difference). I've always thought the App version of a program was a dumbed-down "lite" version of a bigger program. So, if I buy the $79 app it will be the same as the $200 program?

There may be two differences here. First semantics. The word App usually refers to a program for a smartphone or tablet device and by nature these have to be smaller with some limitations (e.g. Keynote).

The term for a program or software is Application, and some people shorten this to app, so this could create confusion. There is no app for Aperture. The $79 version of Aperture is exactly the same, but does not come in a box, it is a direct download, there is no CD. Also missing are some trial libraries of images (I never installed these anyway).