From the standpoint of legacy...
I got the feeling that Bill is really done with his work and that he will take the back-seat and focus more on what he can do with his money for life. After all, he made it. He has more money than most of the worlds countries. The guy, or spirit if you will, at Microsoft that most mac lovers hated has moved onto Ballmer as he now has the reins at microsoft and wants to make a legacy for himself as Bill did while also getting out from under Bill's shadow.
Likewise, Steve is still making his legacy. While he and Woz did make the worlds first real PC, after leaving Apple Steve was really on the outside until 97, after witch Bill was on track to be the worlds riches man. Steve has a few years left to catch up with Bill, as he was never fired from his role as CEO at Microsoft.
Bill's legacy really comes not from having done anything revolutionary, but the shear marketshare and wealth, with all of us looking on in amazement as the industry grew to encompass everything from computers to our freezers. Bill will be remembered for being a great software engineer that allowed him to become the wealthiest man alive, which in turn gave it back to society, as a good steward should.
Steve will be remembered as the man that changed the world with the introduction of the personal computer that changed how we all live. The problem with defining Steve's legacy is that we cannot finish it with the line above, as Steve is not done. He is not focusing on the digital hub as most see it, but how a society lives and evolves and the best way to enrich the experience of life. First with computers, than the iPod, and now the iPhone... which is still a far cry from his vision. It may be a few more decades before we can truly write the full extent of Steve's legacy, but you can be assured it will be about radically changing the way we live or lives.