Yes, dips are much easier for individuals who weigh less. This is particularly the case for individuals who weigh less and have lower body fat levels, since any additional fat you have is making the lift more difficult by increasing the load, and at the same time, because it is fat and not muscle, it is not adding at all to your ability to lift the increased weight. The same could be said, however, of individuals with a lot of muscle in their legs/lower body, since it isn't contributing to the lifts.
Nearly all of your body weight is being moved when doing dips/pullups/chinups. Consider that if you were comparing yourself to a 200 pound individual with the same dimensions as you, he'd have to do roughly 33% more work than you just to do one of these body weight lifts.
Consider that a typical males in their teens/20s, even in an untrained state, who are 150 pounds or under, can walk into a gym and probably bang out quite a few dips. The same can't be said about individuals over 200 pounds, who may not even be able to do 1 full range of motion dip in an untrained state.