I would hope they have a sense for how many they can hope to move daily based on past experience. No doubt they're counting on a holiday rush to help.
As to the 8 GB storage:
- This is the same as Samsung's standard Galaxy Tab 4 7.0, which is only available in 8 GB variants from what I can find. Considering how many years Samsung's been pushing 8 GB 7 inch tablets, I suspect they have a feel for what the market wants in an entry-level device. I still get plenty of good use on my old 7 inch 8 GB tablet.
- My Samsung Galaxy Note 10.1 2014 running KitKat does have the Move to SD card option. Of course, not all apps support it, but it's not like a microSD card is useless on a Samsung KitKat device.
It's not for power users. It's for people shopping in a book store who might want to read on a device that the helpful staff at the store can help them with. The specs are on-target for that intended audience. I (probably) won't buy one, but I might recommend one for someone looking to read ebooks.