Are you talking about without the heal guard? That's the only thing I see possibly missing there. Most nerfs you buy won't come with them. AC and Cannondale are the only ones I've seen.
I had a 02 Cannibal with the old square Graydon Nerfs and it seemed slower than my 03 with the new AC slanted nerfs. Must be a wind resistance thing. Aerodynamics will always make you faster!
Actually, I think it has to do with the slanted ones not letting someone else's front tire get hung inbetween your tire and that corner on the older ones. They can be a bear to seperate when they get hung like that!
fyi, it also has some to deal with tire clearance, the first ones didn't have just any too much (they were retrofitted from another make and model) also, changes in styling help sales, we've all seen the "old" style since around '86-'87 when they first came out. Maybe their tooling finally wore out! :-)
Look where the battery is also see how there isnt enough clearance between bottom of the motor and frame to fit a tube.Plus now cannondale has a nice hole in both sides of frame to put the tubing in.Tire clearance.Seems kind of logical what they did.