It is a nice gesture, but I see it more as a setup for the next statement - "...what we focus on is innovating... and somewhat ignore how many horses there are.

It is a nice gesture, but I see it more as a setup for the next statement - "...what we focus on is innovating... and somewhat ignore how many horses there are." He's throwing MS in the race to deflate that prior binary Windows/Mac mind share dynamic being applicable to mobile - that for one to win the other has to lose. In other words, I read that as Tim trying to convey they are more in competition with themselves than with others; that they're raising the bar by their own standards rather than paying attention to what the competition is doing.