Yes, it was Live8, and Yes it was a good cause, but I know that some contracts don't allow the star to just "Take some days off" Regardless of Cause. The Film Studio is given a certain budget, and a certain ammount of time at each location. They probably couldn't afford to halt producion for that day.
And who are we to say that 50 didn't donate, anyway?
Let's not speak ill of him unless we know all the facts, first.