Why is that when I'm standing in a moving double deck bus, my body doesn't move a lot; whereas, in a moving single deck bus, my body moves quite a bit? It seems like I swing a lot in single deck buses, much more than in double-decked buses. Why is this?
Frankly, until you bring along an accelerometer as well as tracking the bus's speed thru corners (I'm assuming you mean you sway during a turn, not just going down the road), I'm going to remain skeptical of your claim. Centripetal force is centripetal force. Now, if you happen to counteract turning force unconsciously, it may be that you feel more "swinging" if the bus floor tilts, and if it turns out that double-deckers are designed with anti-sway, or simply turn at slower speeds for safety, then that's why.
Or maybe it's because you take the double to work, but the single home from the bar :-)