It seems to have more to do with how it's stored than anything else. My 200-gallon tank has a vented cap (which I'll try to eliminate soon, since that tank just got filled again), while the cans are completely tight.
Ethanol or not doesn't seem to really matter, though. When vehicles filled up from the 200-gallon tank started getting cranky, the (regular) gas was about two years old. When draining it, it was a pleasant surprise to see that the ethanol and water hadn't separated out at the bottom. That was with using StaBil.
Basically, because that tank can "breathe", the gas lost it's potency. Thankfully, it looks like Star Tron can at least partially counteract that. Does it work the same in a less dry climate? That I don't know. But if the vessel is indeed air tight, humidity shouldn't matter.