I am not sure why, but it seems (to me) that everything JS does (for charity), is a PR stunt. It's not just her though. There is a whole list of D-celebs that do that as well. It's almost like "Wait a minute. My name wasn't in the tabloids or on ET yesterday. Let's do something to change that!", you know?
I tend to agree with you. Sure it's a nice gesture but there are a lot of people who donate time/money without having a camera crew with them to make sure they receive credit.