Well.. maybe it comes down to therminology. No matter what they are called there is an upper and a lower "intake".
The upper has not only the plenum (large open area) but it also has the runners that go from that plenum to each lower intakes port.
Unless you have heads, cams, and spin it past 6k there won't be a performance benefiet. The stock intake is actually very very good at maximizing low and mid-range TQ for such a short stroke motor.