(Note: I have solved this problem, but it took long enough that I\'m posting question/answer here.)
The Xcode build process \"optimizes\" my PNGs when build
Found another very simple method to disable compression for a single png file. I think this is a better approach than the accepted answer because you don't have to change type (or extension) of file in the local file-system but only in XCode.
Change the file type from Default - PNG Image to Data in Identity and Type inspector in XCode. See below:
Was:

Now:
