What are you meant to do if the child doesn't wake you up? Set your alarm from 5.30am on a weekend? Then click snooze every 5 minutes in the hope that you catch them getting up at some point?
My DS does get up on his own. He doesn't bother waking us up. Although, he has only done this since around (approx) the age of 5. Maybe just before he turned 5. He prefers having the mornings to himself. He gets complete control of the tv, whilst also comes on the computer and goes on Education City for a bit (Albeit, the last part has only been since he turned 6)
Yes, we have got up and found the living room a complete mess with toys, but that has been the worst case scenario. And he soon wakes us up when he is hungry (that is one thing he knows he is not allowed to do. I recall climbing on kitchen sides as a child, falling and splitting my chin wide open and considering all cereals are in the top cupboards, he has to ask us. Nor is he allowed to mess with anything hot) He does, however, attack the fruit bowl upon his awake so he does get that half an hour/hour to have complete control of the living room before coming through, jumping on us and singing "I'm hungry, I'm hungry, I'm hungry, I'm hungry, I'm hungrrrrryyyyy". That is if we aren't already awake.
It really does depend on the child. Some 3 year olds can be more advanced than others and are aware of certain dangers, and what they are and not allowed to do. Personally, my eldest I wouldn't of been happy with allowing him to be up on his own at 3, but maybe I will feel different with my youngest. Who knows?