No. All it means is that, Nadal's style of baseline play works really really well on clay. It has worked much less well on grass (despite impressive achievements) and even less well on faster hard courts. Though you will see more net play on the faster surfaces on the whole, the entire calendar year is more or less a baseline game.
Having a great baseline game is not just about having incredible consistency and durability - attributes of attrition that help one to win on clay in general - but also about how quickly and fatally one can strike, variety, and other things I can't think of right now. In general, faster surfaces favour a more aggressive style of baseline play than the clay courts, hence why Roger Federer has seen amazing success on the courts of Wimbledon and the US Open as well as many other tournaments of faster conditions; his baseline game has likely been superior to Nadal's in those sorts of conditions.
It goes without saying that to win on any surface requires all these properties, but certain kinds of surfaces will lend themselves to some sort of attribute bias.
Having the best baseline game is not just about consistency and durability, it isn't just about who can last the longest and who can defend and absorb the attacks of others; it's also about who can strike the strongest and can strike most frequently in an unanswerable fashion.
Right now, Djokovic has an excellent strength in both the defensive and offensive sides of baseline play. Nadal at his best has more defensive strengths than Djokovic but probably less strength offensively. Federer at his best is quite clearly weaker than both defensively and stronger than both offensively.
In short, the clay = Nadal wins argument is naive, I reckon.
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As an extension to this basic argument, it would be reasonable to conclude that the best baseline players in history are those who have seen the greatest success across a variety of conditions. S & V players can force the issue as much as they like, there's almost always going to be a lot of baseline play in any match. To have major successes on all surfaces you must have an excellent all around and versatile baseline game - one that can adapt fluidly to changing conditions. Going by this, it would be possible to come up with a shortlist of the best baseline players of the Open Era. A list - which is only based on achievements attained during the Open Era (sorry Laver and Rosewall) - might go something like:
Agassi, Borg, Federer, Lendl, and Nadal.
Are these the best of the best? Some names have been left out, I'm sure you will have noticed. Jimmy Connors for his lack of even a Roland Garros final, Novak Djokovicfor the very same reason, and Mats Wilander for not getting close to a final on the faster grass of Wimbledon. Connors did have a lot of success on faster clay variants but on slow red clay he struggled. Though I appreciate that he boycotted Roland Garros out of anger/disagreements for some time, I find it difficult to include him in the very elite group of the very best baseline players in the Open Era.
Achievements attained are ultimately the tangible evidence of excellence from a player, and in this list I cannot include Novak Djokovic. It goes to show that even though we can argue that Djokovic's peak baseline game is equal to or better than Nadal's, ultimately what matters is sustaining those excellent levels. Nadal and Djokovic are roughly the same age, but what has been revealed thus far is that Nadal has been a superior baseline player to Djokovic across the board for more or less the whole of their concurrent careers.
