I don't think it matters at all whether the top stopped or not. That ending is there so that you come to your own conclusion. To me, it works out well because ending on a major question fit the entire plot of that movie perfectly.
When he was on the phone with the kids at the start, the whole conversation sounded like one where the kids think Cobb is away on business. That shouldn't make the kids too much older when he does come back. The timeline gets all screwy too since he has spent so much time in dreams, especially limbo. So it can seem like a long time to him, but in reality only be a couple months.
The one thing I liked about the scenes with the kids was that every time in the dreams, they never showed their faces. He only got to finally see their faces when he came back. My memory of those dream scenes may be a bit off, but that's what it seemed like to me.
edit: Oh, and the thing in that movie that I had the hardest time getting my mind around was watching the kid from Third Rock from the Sun shooting guns and kicking ass.