Why are ethanol piston engines apparently cheaper to maintain than avgas piston engines? In the course of hunting for examples of 100% ethanol-powered piston engines, I found the Embraer EMB 202 from Brazil that is modifiable to be that way.

But the article also says "The alcohol fuelled Ipanema engine also has 20% lower maintenance and operational costs." (no citation there, howerver.)

I also found this PDF that says similar things:


  Avgas is slightly cheaper on a per-kilometre basis than ethanol, but the lower maintenance costs associated with the use of ethanol ultimately make it a cheaper fuel option for pilots.


Why is this? What exactly are the modifications made to normal engines that somehow reduces operation costs? And why aren't these modifications made to normal engines that just keep using avgas?

(Please: let's not get into an off-topic argument about whether ethanol should/will replace petrol products. I already know avgas is about 40 MJ/kg and ethanol more like 28. This question is not about that and I hope it doesn't become another casualty in that flame war.)
Apparently a study was run for the FAA at Baylor University and it found that Ethanol caused less wear on the engines. You can trace the bibliography for quotes on the study. They concluded after testing for the O-235 engine 


  The relatively low wear and general engine cleanliness indicates that
  the engine can operate on ethanol fuel for longer time periods than on
  100LL avgas. An additional test is planned in which the engine will
  run according to the schedule met in this test, except for 300 hours
  rather than 150 hours, to justify an increase in recommended TBO for
  the engine operating on ethanol fuel.


The FAA also ran a wear test on E-85 that you can find here. Their summary is mainly about whether or not it works which it seems to, they don't touch very much on wear. Still worth taking a look at on the topic. 

It does seem that ethanol can increase engine life as has been seen in current testing.