They're comparing the 300zx front aluminum calipers to the 300zx front iron calipers. Nobody is making any other references to aluminum being an issue with calipers in general. Z32 calipers were designed on the 80s, and since that doesn't seem to mean anything allow me to highlight: a vast amount of time has elapsed since the 1980s where R&D has gotten the better of our dinosaur caliper design. If this isn't making sense I'd start looking to trade your Z in for a Honda.
Cheers, JBrobst
"A life spent making mistakes is not only more honorable, but more useful than a life spent doing nothing." George Bernard Shaw