Here's a link to an example capx
(sorry I need to split the URL below because it does not allow me to insert links into forum posts yet - I don't have enough reputation).
If you press "w" the player accelerates to the right.
If you press "left arrow" the player rotates counter-clockwise.
If you press "up arrow" the player accelerates toward self.angle.
If you try pressing "w" then "left arrow" and then "up arrow" you'll see the player move in the direction the player is facing.
If you try pressing "w" then "left arrow" and then "w" you'll see the player continue to move right regardless of where the player is facing.
So, there's clearly a difference between the two. I don't know what "Forwards" keys off of. It can't be the angle. Perhaps it's just the direction of the sprite when it was inserted into a layout?