A tax exemption is not a subsidy.
You sound like Clinton redefining "alone" and "is".
If the Federal Government gives money to, or waives taxes of one product over the other, it is a subsidy.
The American Heritage® Dictionary of the English Language, Fourth Edition, disagrees with you.
1. Monetary assistance granted by a government to a person or group in support of an enterprise regarded as being in the public interest.
2. Financial assistance given by one person or government to another.
Tax breaks are monetary or financial assistance. Having ethanol users not pay their fair taxes for the roads on which they drive is something we can agree to disagree upon.
I stand corrected. Wrong terminology, same idea.