The extra fluid will help build the pressure to keep it in there and since the path of least resistance will come from the air pulling through the master cylinder, you very well may be right, we're just doin it "by the book". A couple things you can take into consideration is the operation of a water tower, where pressure from above will force fluid down. Once a valve opens water goes out, but if you had a valve that led above the height of the water level in the tower, nothing will happen when you open it. Then there is taking a cup full of water, putting a piece of paper ontop, then flipping it over and watching all the water remain inside trapped due to the pressure. Sounds like both these amazing truths of physics are taking play here.

As for blowing my explanation, nah man, this is a forum all opinions should be respected, unless of course they're unanimously deemed as BS. Honestly I'm really tempted to try this myself because if I can do without the 2 40lbs weights when doing brakes in my truck... F YEAH! It's such an annoying process.... Pump brakes, set weights, run to screw, open, close, rinse and repeat.... gets irritating after the second brake and you got two more to go.

 

Yeah, go ahead and give it a try. I always thought that was the purpose of putting a little bit of brake fluid on the bottom of the jar.
Here's the funny thing, I was at Harbor Freight yesterday and I picked up a brake bleeder (pictured below) for $20. I have to do the yearly tune-up on my car, and I thought I'd give it a try. It looks & feels like it'll do a good job. Might be better than using a pair of 40 lbs. weights



Another funny thing is, you'll see this same pump marketed under different names for about three times the generic price. The only difference is they'll put a sticker on it.

 

Hi Guys, I have done the brakes both ways and both ways work well. If you have someone to help with the car or bike then have someone pump the brake untill hard and hold brake on with pressure. Crack the bleeder screw for a second and tighten. Repeat this untill the brake is no longer mushy or soft (if there is air in the system it will compress and feel spongy). If you are by yourself attach a tube to the bleeder screw and put the other end in a jar with new brake fluid, crack the screw and slowly pump the brakes. This will force out the air and prevent air from re-entering the system. I usually use the 1st method, its less wastefull (you shouldn't reuse the fluid in the jar) And the kids always like helping Dad as they stand on the brake pedal with both feet! I have also used the jar and fluid works just as well. Can also be used to bleed your hydraulic clutch.

 

Just a heads up on that bleeder pump I bought ~ it sucks. The pump itself works good and it's built well, but what ends up happening is that it draws in air from under the bleeder threads, so the fluid you extract is all foamy, plus it takes forever. Ended up calling the wife in and doing it the old way.