the power glide has an offset cam that adds speed and power of the beater at the end of the stroke. the rolling glide has a continuously curved cam that keeps the speed and feel of the beater the same throughout the stroke.
as for the eliminator, thats great if you like the pedal. but think of this: how often are you going to change the cams once you find a feel that you like? its cool to have interchangable cams but once you find what works best youre going to have 3 sets of cams that are just sitting there...with the cobras you just have to know what you like before you buy it. ive never had a problem with my cobras.
i think the cams are more marketed for the guys and gals that play more then one style and can't afford to have alot of pedals for each one, but you do have a point, i would most likely just use one cam all the time if i bought them, i guess next time i get the chance (techniqually i've never had the chanch) i'll see what the majore feel difference between the two brands are