So is this about the weight savings then?
You are of course correct, and while the stat sheet junkies will dismiss the 2 or 3 lb difference...the final judgement will be on how heavy the bike "feels", just like comparing an 05/06 WR450 to a (dare I say more truckish?) earlier model of similar weight.
At the end of the day all of the 450+ 4 strokes when outfitted similarly(i.e. estart, potection, SA, damper, etc) all weigh close to one another. I agree that the "feel" of that weight depends on a variety of factors that include placement of mass(centralization) and motor inertia characteristics.
I will gladly sacrifice a few pounds to a 450/525EXC to get superior suspension and handling which is what the 07 WR's promise.
It seems that Yamaha has done virtually everything possible to make an EXC killer , but failed in getting the plate for California(I can live without it).
BTW: Did anyone notice the difference in weight (DRider article)of the Akrapovic Ti system weight to stock? 5.2 to 8.92. That is a pretty huge drop if true for a single accessory.