The French taxation system means that if he is paid a salary in France, then he becomes liable for tax at 75% on his total worldwide earnings as well as social security charges of up to 20%. I Do not blame him for making his salary over to a charity but it is not quite as benevolent as it is made to appear!
Especially when you factor in the money he will make from the tacky merchandise and image rights which will be taxed in a lower bracket... the fans of his seem to forget this.
Beckham is quite a hard, calculating individual behind the facade. I wonder what he likes more.... fame or money-making?