Getting back to the OP, it's worth mentioning that on many aircraft, it is necessary to hold opposite aileron in a steep turn to prevent the plane from rolling more into the direction of bank. This is because the outside wing is moving faster through the air, hence more lift. I have noticed it most in high-wing, non-aerobatic types (Cessna singles, mostly). "Sporty" aircraft like the Grumman low-wing designs aren't as noticeable. I will say that I don't notice it much on RC aircraft. I think part of the reason is that our planes tend to be light and over-powered, and generally fly very fast. This all means the plane tends to not rotate about its yaw axis as much when in a bank (especially sport and pattern aircraft). To see the other side of this coin, try slow-flight in a real plane: very shallow bank angles result in surprisingly fast turn rates. The plane will also tend to try to roll into the turn on you (again, varies somewhat by aircraft type).

I seem to recall this roll issue is less pronounced on aerobatic types, such as the Decathlon (semi-symmetrical airfoil, very little dihedral)....although it's VERY noticeable during hammer-heads.

Matt