You can find before/after vids on the interwebs, but the difference is actually greater than sound in the videos capture. Maybe this is what they were thinking: it's analogous to having wheel covers over steel wheels that look like racing wheels. Somebody at VW (it's actually an Audi part that also appears in the TT) thought they were being clever by using an acoustic rather than a visual ruse. The BMW m5 also plays recorded engine sounds, by the way. Here's a car and driver article about it. http://www.caranddriver.com/features/faking-it-engine-sound-enhancement-explained-tech-dept
I suppose they are also trying to please car reviewers who like to say nice things about how sweet the engine sounds. More nice things said by reviewers means more sales.
I HATE the idea and everything it stands for, and based on what I've read I'm not alone. The people who want their cars to sound louder generally only want that as a sign of some performance benefit. Everybody else should want the lowest noise floor possible. It's easy to think of why: music sounds better, communication is easier, emergency vehicles aren't masked, stress is lower, the Bluetooth microphone works better, your can hear what's actually happening in the engine like the cool sound of the turbo whine and so forth.
One of the few complaints about the car until now was the overly-growly engine. My wife's Passat had the same motor, and I always wondered why mine was so much angrier sounding. I put up with it and ignored it because I thought there was some performance or cost reason. In fact, VW spend good money on making my car noisier and my stereo sound worse!
Oh, and VW, please explain this: "you can't fake fast" advertisement. http://www.golfmk6.com/forums/showthread.php?t=40486