It really depends on how low or high your keyboard is. I keep my keyboard on the keyboard tray, so my thumbs press flat on the spacebar with it in the stock position. I do no use a wrist rest, but I do try to angle my hands and fingers less flat than seen in the video above. On my higher keyboard, which is an Apple aluminum BT, the spacebar and all keys are flat anyhow. It's also substantially thicker.
I tend to think flat keycaps are better anyways. If the edge of the spacebar key is bothersome to you, then it's possible the edges of all the keys (particularly the corners) are as well.
Another thing to consider is the fact that so many people enjoy the feeling of flipping the spacebar and some/all other keys on their boards.... goes to show that the standard keycaps really aren't designed to be particularly ergonomic.
