Chronology alone makes Shuttleworth's claims for Unity hard to accept. When OS X is eleven years old, and Unity less than two, how likely does it seem that Ubuntu could have developed into something better? Compare the relative resources of Apple and Canonical, and the idea seems even more implausible.
Something, too, seems ungracious about claims to have surpassed software that you have modeled your own so closely upon.
All the same, Shuttleworth's claims are harder to dismiss than skeptics might expect. Although many of Unity's design innovations are mostly minor and some are controversial, Unity does have more original features than many admit.
On the other hand, if you value an interface for its configuration options, and its ability to meet the needs of users with varying degrees of experience, then you are more likely to conclude that Unity still has a ways to go before it can match, much less overtake OS X.
Choose your assumption, and the conclusion soon follows.