Ravens/Steelers game

[zm1283]

Steelers DB lights up Willis McGahee after he makes a reception over the middle. McGahee fumbles and it's ruled as such (right call). Looking at the replay, it was CLEARLY a helmet-to-helmet hit and there was no flag. Why no flag on this, but NFL referees will throw flags for much more minor things? (D-lineman's hand accidentally brushing a QB's head while trying to deflect a pass) I thought football referees have time to "Watch the play develop"? If they have so much damn time, why can't they get stuff like this right?

Edit:

http://www.youtube.com/watch?v=QfS9KQsExgs

(This one really takes the cake!)
http://www.youtube.com/watch?v=d9KmXAmMTjw