The GTI makes 250+ lb-ft of torque at like 1400 RPM? With an engine as stout as that, gearing is less of a concern. You could have a 5 speed and it will still feel pretty strong.
The 2.5 NA engine, feels strong/torquey at 2800-3500 RPM, then feels flat until you get to like 5000+ RPM where it makes the most horsepower. So a transmission with more gears could allow Mazda to keep the engine in its powerband a lot better. However with the coming of the SkyActiv-X engine, this is probably no longer a concern for Mazda. If I'm not mistaken, some reviews mentioned how gearing is less of a concern with the new engine because it feels strong across the powerband.