I asked Professor Blonder to run some tests to see if the beer actually gets into the brat, or if you need to puncture the casing for it to penetrate. He mixed beer with a green dye that is heat stable and moves through meat in a manner similar to salt. He punctured some brats with a fork, and even cut the ends of a few to see if the beer entered more quickly. When he removed them and sliced them open, the dye had clearly penetrated 1 to 2 mm, but surprisingly, the depth of penetration did not increase much whether they were simmered for 15 minutes, 30 minutes, or 45 minutes.
Also, the beer did not penetrate bare meat on the cut end or through punctures any more than through the intact casing.
The conclusions: Simmering in beer actually does add flavor to a thin band of meat under the casing; puncturing with a fork does not accelerate the penetration (but does cause the brats to shrink a bit); and simmering for 15 minutes is nearly as effective as simmering for 45 minutes.