It's the complex dextrine chains that cause farts, which is why beano helps. Beano breaks down starches, it doesn't kill yeast. Commercial breweries have much more efficient mashes, hence the fewer residual starches in the beer.
Sure maybe yeast can survive your stomach acid, but it will not thrive. Downing a few thousand yeast cells will not cause adaptive and primary phases for fermentation. Consider this food for thought:
I have a Maibock that gives me righteous gas. This maibock has lagered at 34F for 14 weeks, it's crystal clear. I'm positive that if I tried to bottle condition this beer, it wouldn't work. There is not enough live yeast in the brew, and it's a common occurrence to add more yeast when bottling lagers.
However, this maibock recipe calls for 16 pounds of grain, and with my mediocre mashing skills, that leaves a ****load of complex starches in the wort. This is why my maibock gives me much more gas than say my hefeweisen, which is full of live yeast.
To reinforce these facts, I'd bet if you drank an all-extract brew, no steeping grains used, you'd have no flatulence. It's the mashing-at-home that causes our beer to contain the complex starches that our body can't break down. Can anyone attest to this?