Just wondering if there is a point to bleeding the brakes if the system is never opened, since it's effectively a closed system. For example, does the chemical change should the fluid reach boiling point release gas? Or should one change the fluid periodically because of some type of degradation, which really falls under the category of flush and not bleed, but the process is similar from what I understand.
Brake fluid by nature is hygroscopic, meaning it absorbs water. Even though it is considered a closed system, it doesn't mean it isn't hermetically sealed. Brake fluid will absorb water, have no doubt. You should change your brake fluid once a year or there about.
As the brake fluid absorbs water, it becomes less tolerant of heat, meaning it boils at a lower temperature. When you step on the brakes, you are exchanging motion to create heat, which the brake fluid must be able to tolerate. Here is a chart of the different DOT's used for autos (pulled from this Wikipedia page):
Dry boiling point Wet boiling point Viscosity limit Primary constituent DOT 2 190 °C (374 °F) 140 °C (284 °F) ? Castor oil/alcohol DOT 3 205 °C (401 °F) 140 °C (284 °F) 1500 mm2/s Glycol Ether DOT 4 230 °C (446 °F) 155 °C (311 °F) 1800 mm2/s Glycol Ether/Borate Ester DOT 5 260 °C (500 °F) 180 °C (356 °F) 900 mm2/s Silicone DOT5.1 260 °C (500 °F) 180 °C (356 °F) 900 mm2/s Glycol Ether/Borate Ester
Brake fluid also needs to be changed to reduce corrosion in the brake lines.
You are right in that the process is pretty much exactly the same between flushing and bleeding. If you change a part which requires you to bleed your system, you may as well flush it while you are at it.