I do not agree that it is a small percent of people only in the forums, since by premise of a bubble, a bubble is a small sample of the population. The issue is bigger than the forums by mathematical default and without any need to exaggerate with an exponential extrapolation. I prefer polynomials, since tends to have less regressive based bias
Sales mix of the S3 32Gb ranged from 10% to 15%, so just from that and the less storage of the S4 and app size growth (and content and OEM marketing of 3D games)- it has to be higher than that now. Going by pur apparent "knowns", my guess is the impact in a few months is up to 25%, since will take time for some to start the app juggling and others to appreciate they were duped about putting apps on the sd card. Why have a fancy chipset device and push high data content if you can not use it? That will be some folks practical conclusion, but the issue would be reduced by offering larger storage models.
Weighted impact will probably be 15%, since even though some bought the 32GB, that does not mean all used the storage.