I may be wrong, and sHTiF probably knows better details, but I don't think you guys want to confuse the issue by talking about the total size of your original pngs as they report in the filesystem and the speed at which things load in your app and on mobile.
Remember that if you are using pngs right now (as most of us are) Flash/AIR is going to load these into fully hydrated 32-bit 8888 BitmapData objects and send them to the GPU as this bytedata.
I could be wrong, but I don't think the majority of the time you are seeing in loading assets has anything to do with how well you are compressing your original PNGs or whether you are removing unneeded embedded color profiles etc...
Don't get me wrong, compressing these initial PNGs definitely improves your total .ipa/.apk package which is a benefit, but I don't think it should be discussed in the context of improving startup times.
Maybe there is some portion related to faster PNG decoding of the files initially, but I am not sure that is very significant.
(Hence, why the compressed format ATF will be allowing the upload of the compressed data to the GPU to combat the load times that we see in PNGs)