there are many ways a head gasket can blow, the use of a compression tester is used in the case of the cylinders leaking between each other i.e one cylinder will read very low because the compression is leaking into another cylinder, it's an easy way to diagnose one variation of blown head gasket.
and the part with seeing if your leak down test for detecting a leak into the water system, hence why we use block checks, run the car up to operating temp so that the thermostat opens and bung it in... alot easier in my book but then some ppl do prefer your way of doing things as well
and can you please break up your posts as they're very hard to read when they're all together