Preconditions are saying the chairs must be green, or that crab cakes should be served or no deal. Parameters establish what you will actually be discussing, and its hard to discuss borders of a state that one state keeps gobbling up. It's that simple. Besides, Israel needs to follow international law just as a matter of justice, abiding by which is necessary, and not a precondition.
Clashes between IDF and protesters in Bethlehem and East Jerusalem (Reuters)
from the article: Palestinians: No talks unless Israel accepts preconditions