it's basically there to be one of the aesthetic differences in trims. Wimpy base model with single exhaust vs turbo version with dual.
The '14 turbo model has the fake dual exhaust also. It just makes the Forester weigh more and IMO provides no value.
Maybe for the '15, Subaru will provide 6-inch diameter chrome exhaust tips, four of them, or hook up the audio system to the engine speed and provide a deep V8 rumble with a switch to output the torn canvas sound of an un-muffled superbike at 14,000 RPM.