I preffer a series of concerts for charities like the MK and friends 2002 than this private posh things...
But I guess its less work to play 5 songs (that he really played so often that he doesnt need to rehearse anymore) in front of a posh audience that doesnt matter about the real quality of the perfomance that rehearse seriously for several concerts in front of an audience of fans...
I have a simpler explanation : this is not a choice, Mark was just asked to do it and he agreed.
And, at least for the last two ones, Mark's RAH run were also charity gigs, in front of 4 000 fan every night.