Filip brought up in one of his postings the issue of the FIRST Lego League competitions mixing RCX with NXT... got me thinking...
I was looking over some of the designs that can be built with NXT and it occurred to me that there is a SUBSTANTIAL amount of empty space - compared to the RIS and block building.
When it comes to weight, a lot of RIS designs were underpowered by the standard motors. A portion of my design time with the RIS system involved reducing weight; an unfortunate side effect of some of my designs (and maybe yours, too) was that I was forced to reinforce a weak point by building up that area with extra bricks. This hurt my designs in multiple ways, the main 2 being it looked ugly and it was heavier.
With the NXT Technic components, I'm sure weight will always need to be considered, but... look at the empty space of the beams and angled pieces. You'll see holes... LOTS of them.
I realize you cannot compare an NXT bot to a RIS bot - apples to oranges in most cases. But when considering form versus function, it might be interesting to compare 2 bots that perform the same function and weigh them. This may not be that big of a deal, but if the NXT motors are more powerful and the NXT components are even 20% lighter (or more!)... well, think about things like competitions.
If the function is the same (the competition's tasks to complete), but the form is faster, lighter, and more sturdy, are we going to see NXT sending RCX to the bench?