You misunderstand me. Just as much waste will be going to the landfill... you might keep your current phone for two-three years and then dispose of it in one piece. With those cheap, quickly changed components, you'll be throwing those out every few months so the end result is the same amount of material being disposed of but spread out across two-three years.
I want my phone to be small and robust. With all that space (and weight!) being taken up by the plug system for the modules and the locking mechanism, the phone is going to be bigger than it needs to be and how well will it cope with being banged around in your pocket?
My iPhone is one little, compact, well put-together unit because they don't have to worry about making any parts removable and so they can pack everything in really tightly and be creative with how everything is arranged inside so it all fits in together.
I understand the theory of what they're trying to do, but that's why phone manufacturers make more than one model of phone! Do you want a big Galaxy Note 2 or a little HTC or something with a full keyboard to type faster?