I tend to disagree here. Well actually you're right when you are talking about these free sites.Personal media (hard drives, memory cards, etc.) are very affordable and much more reliable than some server off in cyberspace...
Still, a backup in the same house on an external disk is not a backup. When your house is on fire, you still loose everything and harddrives are notoriously unreliable for data loss, not to speak of memory cards which are even worse. Cloud storage however uses distributed storage which is virtual unbreakable. Especially when they are distributed globally like Amazon's. So it does make sense to store your data with a party you trust if data is important to you.