1. The earth spins around an axis. Its geographical ends are two poles i.e. North and South. If you travel from any circumferential equator point towards any poll the North and South will remain constant and that is not the case laterally with East - West. This throws out East and West due to lack of constant reference point. The poles make it easier for aligning.
2. The drawings would begin from 'Top' to 'Bottom' i.e. From 'North' to 'South' and not reverse logically.
3. It is accepted practice.
4. By the way, the North indicated in drawing is very rarely true or geographic north. It is plant north and it is mostly any direction other than north :) . This is rather very good example of Engineering common sense. If you really want to test it, try drawing some isometrics with respect to actual North.
