Yeah, I'm not convinced of that "opens the thermostat" to get to the other side stuff either.
The problem with water, salt or fresh, is that you can't thoroughly prevent scale buildup no matter how well you flush. The minerals in the water, and there can be almost as many in fresh water as in salt, tend to "plate out" on to the engine components when the engine is at it's hottest. This causes a "bond" to the surfaces of the engine cooling system that is almost impossible to break down without using mechanical action like scraping or wire brushing.
I learned a long time ago in tech school that a 1/32" layer of scale deposit on an engine cylinder head has the equivalent resistance to heat transfer from the metal to the coolant of approximately 1 1/4" of solid steel. Pretty impressive insulating factor for a thin sheet of water deposit!
And, even in a closed cooling system, using fresh, distilled water treated with a veritable "witches brew" of chemicals designed to lubricate, inhibit scale and prevent corrosion, scale deposits still occur due to the heat.
So I'm with you, some things just need to be taken out from time to time and cleaned or replaced.
Giterdone!