The applications can be shrunk by about 30 - 40 kb by using a PNG optimizer, pngout or Optipng.
Pngout seems to do well but you will need drag and drop onto the executable file by file.
You can use FileMenu Tools and set the Multiple Instances to sequential so that you don't need to drag and drop 40 or more files.
website of pngout: http://advsys.net/ken/util/pngout.htm
This was discussed earlier, but we decided against doing this. The space gained is nearly inconsequential for most apps. And some have shown problems with certain PNGs... this is because some apps don't have full PNG support, just enough for their own images, and if you alter them, they don't load. Manually checking that all images load in apps that have them scattered (for toolbars, splash screens, wizards, game graphics, etc) is prohibitive and the effort doesn't justify the benefit of saving a few KB.
Sometimes, the impossible can become possible, if you're awesome!