It's the same kind of issue you see with a full blown desktop OS, like with the Surface Pro.
But it's odd to see so many people touting the microSD card slot as an advantage of the S4 when you really don't want to rely on that over onboard storage as all apps can't use it. And it's bad when your phone is reading 9GB or less free, especially on a premium high-end phone.
I don't think the OLED screen is a problem, though. I haven't done a side-by-side comparison of it with my HTC One, but it doesn't look bad from comparison shots and my prior experiences with OLED. But it would be nice for the new superfans of the S4 (not all S4 users, just a vocal segment, much like the Apple fans that preceded them) would at least acknowledge that the One, Sony Xperia ZL, and some other phones on the horizon are real contenders. So many users are defensive of the plastic, TouchWiz lag (at times), and the random features Samsung has implemented. You have to give Samsung credit where it's due - it has a great camera, 1080p screen 5.0" screen, and the S view cover seems neat - but the lack of space is not a feature.
The S4 is still a "superphone" because of the specs, but I think Samsung gets away with a little more because of its new-found dominance of the Android market; they'll beat HTC's One with sales even though I *personally* feel that it is a better phone and a better value. HTC, LG, and Sony don't throw as much into eyetracking and other gimmicks (Nokia hit the nail on the head poking fun at the tap to share feature Samsung used to advertise, which I've never seen done in real life) or marketing so they really have to struggle to compete on the overall aspects of their phones. Samsung packs the fastest CPU, but it doesn't help if you have to remove all their crapware to take advantage of it in anything but synthetic benchmarks.