To answer your question, Euphoria is a true physics engine. When a tackle happens in Madden currently, it's just a series of animations to make it look like a tackle happened. Yes the game does have a physics engine, but as someone said it's an EA engine and it's actually kind of rudimentary. To me, it doesn't simulate a tackle, it's more of just a problem solver (like, oh crap two players are colliding, I better do something!) What it comes down to is how well EA can make it look like the two or more players are interacting, and we have seen the result...
With natural motion, a game has a true physics engine. It's the latest and greatest technology and while EA's engine is struggling to get 3 players to interact in a tackle, natural motion can probably simulate both teams interacting if that were possible. Another thing natural motion features is called predictive physics. Let me give in an example. GTA 4 uses natural motion. Lets say my character is standing on a ledge in the game and I fall off the ledge. With an old physics engine, a programmer would have to program my character reaching up as he fell to grab the ledge to try and hang on to pull myself back up to the roof. With natural motion's predictive physics, my character reacts to his environment automatically and grabs for that ledge without any programming from the developer. Now I am not sure how this would work for Madden, but imagine if a 4 man gang tackle was just built into the engine instead of the two years that EA has spent building what we have now, which is really only a 2 man tackle. To go further, it is due to the lack of a decent physics engine that we have NEVER seen a pileup in Madden.
Now lets talk that "other game", it had an emphasis on physics versus EA's emphasis on motion capture. Motion caputure is actually taking guys doing the movements and captuing their moves to the letter via a computer. Ian has even asked which technique people think is more condusive, but I can't imagine that people even thought that captured moves is the answer. THAT is the reason we keep seeing the same 5 tackles OVER AND OVER AND OVER AND OVER again
He argued that physics make players look a little rag dollish and dead, but THAT CAN BE TUNED and I will definetely take that over what we have now. To further the point, with all of EA's emphasis on motion capture, why is it that we don't have signature animations? But I digress, this is not meant to be a negative thread. There's your answer anway.