If you read the article, he says that the DL data are estimated they don't break out all the mainline data.

Somebody must have told the author about this thread, because there's now a correction posted with UA showing PRASM-CASM margins below DL and AA. Here's what he wrote:

"We discovered that we inadvertently used consolidated (mainline + regional) data for a couple of Delta and United's cost lines. These have been corrected, and we've re-verified all the data for all ten carriers. However, some items may not match press release or Form 10-Q statistical summaries because of calculation differences, e.g., Hawaiian didn't include hedge costs in its stated fuel expense per ASM. We calculate everything independently using raw expense and ASM data in Form 10-Q, instead of relying on summary disclosures in press releases. (This is partly to avoid inaccurate comparisons to custom metrics like Delta's "CASM-Ex" that also excludes profit sharing and "special items.") ASM truncation (e.g., "xx,xxx million") in airline releases can cause our calculated per-ASM data to vary from airline summary data by up to 1%."