One small correction before I dive in,
"Abstract art, the term describes art that depicts real forms in a simplified or rather reduced way - keeping only an allusion of the original natural subject."

Therefore abstract art must depict or imply real forms, so an abstraction not alluding to any original subject IS NOT abstract art.

Abstract art falls into two categories, the first of which is--

1. Random
The artist throws a rock through a window or slaps dots on a canvas. No thought is put into it, the artist knows nothing and cares nothing for the principals of artistic design. "Vola`! Give me money for my masterpiece!" Not legitimate art, in my humble opinion.

2. Thoughtful
As my former art teacher the great Tony Ferguson said--
"You have to Learn the Rules Before You Break Them." (that was before he was ousted by a bunch of lazy students, but that's another story) I have no respect for the former category.
The point is, “What am I trying to communicate.” not “how much can I sell this crap for.” The basic artistic principals of Contrast, Color, Shade, Negative Space, ect... all can, and should, be applied in abstraction. I have great respect for any artist who chooses to use abstraction as a medium to convey his work-- and to create something of substance and meaning. Art shouldn't be limited by what you can see. But at the same time It needs to have a purpose, a goal, a idea, something to distinguish it from nothingness.

There is more than two categories. This is highly biased.