The apk build process is case sensitive. I'm sure many of you know this and it's probably documented somewhere, but I couldn't find it, probably because I didn't know the right thing to search for until after I had figured out what was going on.
I spent almost a week trying to figure out why my app worked when run from the IDE on Windows7 but was missing image files in the apk. It was because I had some upper case characters in some of my image file names but I had coded them in all lower case. The IDE doesn't care, probably because Windows doesn't care, but it's important for the apk build process because it will be unpacked on android, a case sensitive file system.
Hopefully this will save someone else some time!
W7BIT
Gilbert, AZ, USA
Proud U.S.Navy Veteran