If I were running the festival, I'd put Modest Mouse on the billing above How to Destroy Angels as well. That's a no brainer. The only reason HtDA is getting such a high spot on the bill is because it's the debut of Reznor's new band live. Outside of a fairly small (but very hardcore) group of fans, nobody knows any of their music, and most people don't even know who they are.
Modest Mouse is a huge band. Even if I don't like anything they've done since The Moon and Antarctic, their first two albums are still awesome.
Rest assured, if it was Nine Inch Nails on the bill, they'd be listed as a headliner... probably even above New Order... which might be something some people would be legitimately sad about.