Indeed, the words can be used in similar ways. But I think I understand how Mr. Jobs meant it. Generally, silly means funny, not serious. Stupid means unable to understand, not very intelligent. Foolish can also mean both of these things. But it can also imply that the person has a certain innocence, a willingness to try things even if they seem to have little chance of success. I am sure that there were a number of times that Mr. Jobs was called a fool and that his ideas were silly or stupid. Mr. Jobs was willing to forge ahead, even when others tried to deter and discourage him. This is a trait that can make us proud of being called foolish.