Why buy a pro or semi-pro camera?

If you are like me, you have wondered more than once why you should pay the extra money for a professional or semi-professional camera if the entry-level model has the same sensor and is much smaller and lighter. There are a few technical reasons like buffer size, speed, autofocus etc. This video also impressively illustrate another reason, which applies if, like me, you occasionally take pictures in rough places — and own a Canon EOS 7D.

http://www.youtube.com/watch?feature=player_embedded&v=RCT-YMgjm9k#t=783