The key is to realize that gravity may affect your trajectory, but it does not affect the forces you feel between your cheeks and the seat.
Imagine the following scenerios:
1) You are flying along straight and level and decide to close your eyes and fly by "feel". Just a moment later, Congress repeals the law of gravity and - poof- it's gone. Would you notice? Well, during S&L flight, gravity is pulling the airplane (with your ass in it) down at 32.2 ft/sec^2 while the wing is trying to lift the whole mess at 32.2 ft/sec^2 (or 9.81 m/sec^2 if you are that kind of guy). Gravity went away, but the aerodynamic forces from the wing did not - so, the airplane will accelerate upwards at 32.2 ft/sec^2 and it will seem that you are being pushed down in the seat exactly as it did before gravity went away.
2 ) Again, you are flying along F.D.&H., but this time, someone pokes the earth with a big space needle and pops the atmosphere. Instant vacuum. Do you feel that? Yes siree Bob! You and the airplane both go into instant free fall (at least until your orbit impacts the surface) and there is no force between the butt and seat.
So, no air, no forces that you can feel. No gravity, just a change in trajectory - no changes in forces. Gravity does not cause the forces you feel when you fly.