Here's what Jeff Sparrow says about corn in Flanders Reds:
He suggests its a source of starch in the wort, and that this is beneficial over the course of fermentation. I wonder if this is an example of Sparrow offering his own interpretation of Belgian practices without really acknowledging that he is. Of course, the fact that it is more typical of big breweries doesn't mean that it doesn't have this effect.
In my opinion/experience/research, corn would only add starch to the wort if it were used in something besides a single infusion mash. If it's sitting in there gelatinized, it will be broken into the same mix of carbohydrates as the starches from the malt itself. I think that is what the quote also suggests.