a) The muscles of the hip can be a little complicated with regard to their attachment points. What I mean by that is sometimes when we are standing certain muscles work to perform a specific action, but when we flex our hips (like in a seated position), different muscles are working. So, you may not be working what you think you are working when doing these machines.
b) Hip ab/adduction is a movement that takes place in the frontal plane as a means to prevent unwanted movement during gait (walking) or other exercise. Training these muscles on a fixed machine (which is in a fixed plane of motion), takes away the stability component of the exercise and doesn't train the muscles to function in the proper way, as they would during real movement.
Lunges, split squats and step ups are great ways to train these muscles instead.
patrick