Assuming you are talking about the Fire(s), I agree with you to a point. For a power user, the limited onboard storage isn't going to cut it. My current tablet is a Toshiba Excite, which has a full sized SD slot and USB host capability, which means storage is basically unlimited.
For certain users, though, who want a simple interface and don't see the need to carry around 30 movies or 1000 songs? These are probably good enough and at the right price.