The previous posts bring up the point that there is reality, and there is perceived reality. I don't mean to get technical here but to answer your question, the reality is, anytime you go around a corner there is centrifugal force applied. The tighter the curve and the faster you go, the greater the centrifugal force will be.
However, the more the Spyder leans to the outside of the curve, the greater the PERCEIVED force will be. Think of the old carnival swings. The faster the ride spins, the farther out the swing and rider go. This is 100% centrifugal force. The same as when riding the Spyder. This same force is exerted on a 2 wheel motorcycle. Which, like the carnival ride, leans into the turn. So you, as the rider, feel it as a down-force instead of a force that is trying to throw or rip you off your seat.
You can scoot your body towards the inside of the turn and lean into the turn. This will convert some of the lateral force into a down-force (as on 2 wheels) and lessen the effect. But this is not a complete solution, nor does everyone want to do this.
The sway bar reduces the amount of Spyder lean you experience in a turn. The greater the centrifugal force, the greater the reduction percentage will be. With the bar kit installed you can actually go through a turn at a greater speed while at the same time experiencing, or perceiving less centrifugal force. And, you can still shift your body and lean into the turn if you feel the need. You just won't feel the need to do so as much as you did before the sway bar install.
But the sway bar does much more than just reduce perceived centrifugal force in a turn. And it is a misconception that you will only see a benefit from the sway bar if you take every turn like Evil Knievel. The sway bar increases the overall stability of the Spyder, giving the driver better control and the passenger more confidence in the ride.