If you do a Google search of "abstract from reality" and read it used in context you will find that it seems to have lost all meaning entirely. However, when it is used, it is used in texts where the author is trying to sound academic while resorting to this worn out trope and/or is trying to talk about other people describing the whole by its parts at a conceptual level in a way that the quiddity (essence) of the thing is lost; it can also mean to make generalizations about the world/things/phenomena from the experience of or perception of the world/those things/phenomena. The phrase "withdraw from reality" is much grittier, a boots on the ground "you may see your grandmother do this one day" phrase, and is often used to describe someone with mental instability and his or her relationship with the world. I recluse or hermit may withdraw from society to a cave, but a psychotic may withdraw from reality to his or her own mind (a personally constructed reality which has not been validated or considered real by others' experience of it). Since the first one should be avoided and has been ground into semi-meaninglessness, I would say the major difference between these two is register and appropriacy. A doctor will not come through a pair of swinging hospital doors to inform a family that their nana is abstracting from reality, but he would put his hand on some crying girl's shoulder and warn her that the more her grandmother withdraws from reality, the less she will seem like the woman everyone once knew.