No one used to switch on Seinfeld, the record-breaking sitcom, just to see its star, Jerry Seinfeld.

Playing a fictionalised version of himself, his role was to act as a foil for more interesting characters. Without his inoffensive patter, however, the show would not have worked. Is that the reason why he has been asked to lead a $300m promotional drive for Windows, Microsoft's ubiquitous flagship operating system?