| Take a look around the welds. Ever see welding with absolutely no heat spots? My guess would be that they weld the flanges on, then blast them to clean up the welds. Aluminum looks like this when you weld it: 
taken from millerwelds.com, posted by KB fabrications. The sport 700 housings don't show any of the discoloration that the surface of aluminum gets when you heat it. My guess is that they look fairly ugly after the flanges are welded on, and require blasting to take off the first few layers of aluminum. The end result is a nicer looking product (that costs considerably more), but who cares what they look like, you can't see them in the car anyway.
********************************************************* Joe GT675RS/Inconel AIM: hoyatiger81
"You probably never even got you hands dirty working on a car. Take care toolbox!" --djtz1
"It's not my fault you went nuts." - Kenny
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