I saw a similar comparison and the numbers I remember were Romney and Barry each at around 13-14% and Newt at about 3%.
The latter is nothing to be proud of, but for the other two, if you consider they each are just about matching their federal taxes with charitable contributions dollar for dollar, you have to comment them for it (and please, let's not go into nitpicking if one gave to a Church and the other to support the arts or whatever)