I don't want to beat a dead horse Joey, but I still have fixtures in the ground from back when FX first came out and was using bare aluminum stakes. They're stilll standing and working. (Granted, they're mostly not exposed to overhead irrigation.)
I think we can agree on a handful of conclusions:
1. Some grades of aluminum are more corrosion resistant than others.
2. A good quality powdercoat process increases that resistance.
3. Some environments (soil type, moisture, salt air) are harsher on aluminum than others.
4. Nothing lasts forever.
Beyond that, everyone has their own experiences that lead them to their preferences as to what fixture materials to favor in what situation, and which manufacturers will give them the best warranty service when equipment doesn't meet expectations for durability and longevity in the field.
So, to go back and address Pete's original contention, aluminum will continue to have a place in landscape lighting, but one must be careful about where to use it, and some will not use it at all.
It's nice to have choices.
Landscaper. Irrigator. Illuminator. Music lover. Coffee drinker.