Yeah, same here with the Armadale line for me - the B sets are somewhat captive on the Joondalup and Mandurah lines. Transperth's excuse is 'the close station spacings on the older lines will damage the motors if the trains have to stop and start frequently.' In actuality, it's more likely an image thing - it makes sense they'd want to run the latest trains on the newest lines (especially a line built to allow higher speeds than what the existing network is capable of handling).
As well, it's more economical to run them on the lines with the highest patronage (Joondalup and Mandurah), especially as all stations on those lines can handle six-car trains, which most stations on the Armadale, Midland and Fremantle lines can't (other than a few exceptions, like Midland and Kelmscott).
Anyway, I've gone off on a branchline here - Adelaide's new trains definetely owe a lot to the Transperth B sets. In fact, another connection to the Perth system with Adelaide's electrification is the new catenary masts being gradually installed in Adelaide appear to be virtually identical to the concrete pylons used here in Perth as well (the original Perth ones were manufactured locally by Delta Concrete, so I have no idea if they're the supplier of Adelaide's masts as well). In any event, they look virtually the same.
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