I think the issue is not really about ethanol being more or less aggressive.
As far as I understand, it _may_ be the fact that ethanol is hydrophile (i.e. "loves" water), through water vapour in the air the dissolved ethanol binds the water, which can then be absorbed by the plastic in the tank. This will lead to an increase of volume of the plastic ... swelling ... spreading. For those who can read german, here's an other interesting summary from ADAC on E10
. So far, the gasoline sold in Germany respects certain standards, see: RACSYSRACSYS