The S3 has one as well and the 32GB sold about twice as many as VZW expected. SD cards do not help much for app installs. The internal space is mapped for the app security core and the data install. SD card does not help and is mostly worthless for apps, but important for media storage.
With app sizes growing, 16GB is quickly becoming like 8GB devices from previous years.
Still, the question is where is the 32GB version? Samsung is offering them, but no sign, unlike for the S3 launch. Answer seems to be Samsung has made a tactical decision to launch earlier than planned.