In that situation, painting the ceiling and walls the same color is actually a classic color strategy. Painting all the angles and slopes and walls short and tall one color evens out the visual landscape of the room. That does a couple things:
1) It will make the room feel a bit more open and spacious because there aren't a bunch of lines drawn around the room where ceiling/wall colors meet.

2) The light will play on those angles and slopes no matter the color. When you use all one color, the shadows and different angles of reflection create a rather neat-o color effect. Just as interesting as using a different color on the ceiling but one color is a more sophisticated approach. Because it speaks to the fact that you knew light would play a part and you knew to just keep it simple and let the phenomena of color & light do all the work.

I also vote for using the same color on everything.

It's easier, and it usually looks better.