I think that's true, but in the case of RPMG (link below) it looks like some of the little guys realized their limitations and formed a multi-plant ethanol and DDGS marketing/trading firm. http://www.ethanolrfa.org/pages/useful-links (scroll down to ethanol marketers). There are at least three marketing/trading firms that don't own plants and I can think of two more.
Good eye and excellent link. Too bad those golden arbitrage arbitrage opportunities just never last long enough for us little fish to get a taste.
One may argue that blend-wall fear pushes buyers (blenders) to pay the price it takes to be supplied with (physical) material. Lack of liquidity on the paper market and possibly large swing in the price of feedstock corn keep buyers with short-term view. On top of that, there have been major logisitical issues since winter 2013. BTW, European ethanol market is even more tricky ...