To a large degree, yes.
That's what many people are finding.
The MPG numbers in the car, don't match what the chemist's predictions say they should be.

Pure ethanol has about one-third less energy.
So on pure 100% ethanol, your car should get 33% less MPG.
It follows that with 10% ethanol, your car should get 3.3% lower MPG.

Many cars get 10% less MPG with 10% ethanol. It doesn't add up.
Thus, the car is messing up and running "rich" and injecting too much fuel.

It is starting to look like at 30% ethanol, a non flex fuel car is able to appropriately adjust. I don't know, but maybe pushing things to 40% will get the car to run lean.

I do not think you should put more than 50% ethanol into a non flex fuel car though. Concentrated liquid ethanol will sloooowly dissove lead and aluminum. It is doubtful it would ever "eat though" any metal parts to the point they fail. It is not corrosive like acid ( ethanol has a pH close to 7.0 normally pH 7.70 to 7.75 on a routine day) and is really very slightly alkaline. Nope. Ethanol will not eat through anything, but the EPA is concerned ( and automakers ) that this dissoved aluminum or lead ( if there was lead solder used to connect any parts of the tank or fuel lines, for example ) will be combusted and go out the tailpipe, and into the air or reduce the effectiveness of the catalyitic converter. Is there any lead in modern cars? I honestly don't have a clue on this one.

Ethanol over 50% will dissolve natural rubber ( but try finding that on your car today ) and certain plastics made before 1984. For any moving parts ( fuel pump ) or things like gaskets that need some lubrication to keep from drying and cracking, gasoline is a thin oil and provides some lubrication. 50% gas is enough to provide those oily properties for lubrication. Less than that ( more than 50% ethanol ) and you start to lose some of the oilyness, and may have problems with perlonged use.

Sorry this got so long... I forget if I already said all of this before on here or not. That's probably more info than you wanted to know!
-John