Tablets are certainly a hot product currently, and the price goes up with the amount of included storage space. The same goes for cell phones. For the same tablet or phone, you may pay $50 or more for an extra 16GB of internal storage.
However, many aren’t aware that when they are purchasing a product that includes internal storage that a portion of that space is dedicated to the operating system and preinstalled software. It could be a large portion of that storage, in fact. For example, it’s been announced that a 64 GB Surface Pro tablet only has 29 GB of space available to users, and the Galaxy S4 advertises 16 GB of space, but only 9GB is available to users.
All tablets and phones will have this issue, although some may a have lesser percentage available than others. In a recent study done in the United Kingdom, percentages of actual storage space  on various products were studied and listed. As you can see, it varies between operating system and manufacturers.
When shopping for tablets and phones, if you are concerned about storage, look for expandable storage options. Just remember, what is listed as built-in storage is not all available for you to use!