Going back to the keyboard vs no keyboard thing, I think it might have to do with the way you're holding your device. You're not holding your device as securely while you have a keyboard out and typing with one or more hands, whereas with a standalone tablet, you're holding it with at least one hand, and the other hand is free to impulsively grab onto it if you think you're about to lose grip. Not to mention that if it has a keyboard, people may be tempted to place the entire device on their lap instead of holding it as instructed.