(I've submitted Combat Imp to Apple and while I wait for approval I'm doing some clean-up which includes verifying problems and writing up radars. There may be a handful of these posts coming up.)
Combat Imp is an iPad only project. Way back when I had just plunked some icons in manually (into the .plist I believe? It's been a while.) As I got ready to ship the damn thing I switched over to using an Asset Catalog for the icons and launch images. I only set up the iPad icons, because why include other sizes that wouldn't be used? And this was good.
At some point later in time I went to make an archive (inside Xcode - I was getting ready to make a beta build for testers.) The archive didn't have the nice icon, instead it had the generic grid/circles placeholder icon. Turns out that even in an iPad only app, the archive uses the iPhone iOS 7 icon and doesn't look for other icons if that slot is blank.
Not a huge deal but I was having some other icon problems at the time and I conflated two problems and went down a rabbit hole. So if your Xcode archive is lacking an icon, try adding an iPhone icon.
I wrote it up as radar 18252465 if somebody wants to dupe it. It happens on both Xcode 5.1.1 and Xcode 6 beta 7.