I didn't get it... Can someone explain? It seems like the walk on the beach looking at rocks is supposed to be a punch line?
It's a mass-produced personalized letter. The content is talking about making a connection with your fans, while the presentation is corporate and distant. There's also an implication that he routinely walks with fans on beaches but looks at disparate objects, or that he cares so little that he glosses over what really happened. It's a joke sent to fans who probably appreciate such a thing considering it's Steve Martin.