White vs. Black iPhone 4S

I recently bought a black iPhone 4S. Last night, I was sitting next to someone who has a white iPhone 4S. I noticed that the speaker on her iPhone has two slots while mine has one. I got curious about it, so I went to http://www.apple.com and the first thing I saw was a photo on the banner page with a white and black iPhone 4S on it. You can see this yourself. The white iPhone 4S has two slots for the bult-in speaker while the black one has only one slot.

Does anyone know why the difference there? Is there any functional difference between the white and black iPhone 4S? Is the speaker on the white model easer to hear than the black modle due to the extra slot for sound to emit? I love my iPhone 4S, so I am asking this question only out of curiosity.