I agree the OS is big. But, I have all the original bloatware and about 40 downloaded programs on my S4 and I still have 8.24 GB left. I can't imagine downloading many more APPS and if I do I'll probably be replacing existing ones. I don't see the storage space with the 16 GB S4 as a problem. BTW, I put my photos and music on my 64 GB SD card. Having said all that, if the 32 GB phone had been available I would have gotten it. Just have to have the latest and greatest.
Knowing how computing tends to work, I really wanted the 32gb model, but it wasn't clear if my carrier would ever have it, so I bit on the 16. Was a bit nervous about that.
First, there was about 9.6 gigs free---not the 8 I've seen reported-- and useable.
Then, I dl'd all my old apps, plus some things I couldn't deal with given my tiny HTC phone in the past, and reinstalled all of them.
At the end of the day, I have over 7 gigs free. Keep in mind, I'm not a new Android user. That's the result of my computing life for 2 1/2 years, installing everything I wanted and had. There seems to be plenty of head room. I do have a 64gb card, but that's largely media storage for me.
I'm still kinda shocked that I can't move apps to the card as I used to, but there doesn't seem to be any big issue so far. I doubt I'll have this more than 2 years, maybe 3 at most. Technology is changing so fast in this field! I think it'll be ok. NOT that I didn't want more space and I would've loved to have had it. Condolences to gamers, but I think most typical users will be fine.
I would note--on my old HTC, there were some apps--suspecting Facebook, G+, among others--that just seemed to eat up everything they were given.
I also note that there is no way to universally clear caches now! You apparently have to do it one at a time on JellyBean?