To go to the poster's original quesiton, I had a situation just the other day where a big burm of snow was plowed behind my X3. I put it in reverse and rolled into the snow very slowly and eventually reached a point where my wheels spun. I then moved back forward and, after confirm it was safe to do so, put it back in Reverse and took a little momentum at the burm. Blew thru it with no concerns about the amount of throttle response available. Definately had power to cause a bit of wheel spin which was then limited by the traction control system.
If your vehicle does not behave this way, I'd question the amount of throttle application/driving technique or get it checked out for any issues.