A computer is something you can use to consume content or produce content.
A tablet is something you can only really use to consume content. (Regular tablet, not artist tablet obviously, and those generally have to talk to a computer)
Your own remark about tablets undermine your argument though. iPads and MS Surfaces have been arguably the best 'artist tablets' and they don't need to be hooked up to another computer.
I know. I think that for many people an iPad (or a surface) are better drawing tablets than Wacoms (cheaper, lighter, better screens) and can very well be used for other things than content consumption. (of course Wacom tablets have their benefits too)
A computer is something you can use to consume content or produce content.
A tablet is something you can only really use to consume content. (Regular tablet, not artist tablet obviously, and those generally have to talk to a computer)