One of the issues that's been in the background but more common recently is the issue of why resistant starch? What's so special? We have other prebiotics and can't we just use them?

Grace ("Dr. BG" Animal Pharm) answers that question in comments, edited below.

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I'm not a physicist but RESISTANT STARCH are DNA shaped carbs. Does that make quantum sense? The energetics and molecular shapes are extraordinary. I don't get it completely, but I know it's inherently what sets it apart from ordinary non starch polysaccharides and obviously glucose, fructose, fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPS)...and our own endogenously produced fuctose which we make on the tips of our microvilli for the microcritters to graze on when food is lacking (between meals? when our genotypes fail to dictate like I'm FUT2(-/-) non-secretor).