I would think the biggest weight reduction would be replacing the stock muffler with a aftermarket one, the stock one is heavy.
Aftermarket A-arms would be heavier. Just as Smooth1 stated, there is more metal in them and they are gusseted and probably use a heavier tubing. Fox Evols on the front would save some weight over the stock shocks.
As far as wheels and tires, I do not see any way to get lighter ones then what comes stock. The stock wheels are not real heavy, maybe a Douglas red label will be slightly lighter. Anything with a beadlock (Hipers, etc.) is bound to be heavier. Stock tires are probably going to be about the lightest tires you can find.
I would bet Wayne Matlock's 700XX is heavier then stock. Adding a-arms, shocks, skidplates, bumpers, rear tool rack, etc just adds weight. Other then the parts he has replaced, there is not much that he has removed.
Plain and simple, the 700XX is just plain heavy. I think it would be very difficult to remove a noticeable amount of weight from it, unless you want to spend LARGE amounts of money. Even then, who wants lighter weight parts on a heavy quad? It sure would be ugly to see your light weight a-arm fold while doing 50 mph.