I actually wondered today who at Google sets their tone/vision?

I think one of the companies that relies the least on a persona for their facade in the market is Adobe.

A valid concern shared by many, but I can't see Apple not being prepared for its CEO's eventual retirement. I think it's safe to say Jobs has shaped the leadership of Apple with people he trusts, and while there's not going to be any one person with his traits, there are enough minds that share his vision to carry the company long-term.