"Power pipes" -- another marketing term. Today's cars are quite sophisticated all the way around. You'll note that the performance guys are having a harder and harder time improving on the factory bits. The new Corvette is giving them fits -- very difficult to find any additional HP with the traditional bolt on bits.
Besides - the factory doesn't just focus on HP - they've got to balance that with emissions, fuel economy, making it buildable, holding up to keep warranty costs down, and keeping overall costs of the product down. The fact is that you have to bump the HP way up for one of the large diameter 'power pipes' to be an improvement over the stock Stang air box with the silencer removed and a flat panel
K&N installed. Even the Fox bodies were factory equipped with "CAI".