Well, there would be a significant difference between the teams inasmuch as the Spurs group that lost last season to the Mavericks has also performed well enough in playoff situations to win an NBA le. It's not a 3 vs. 0 argument; it's a the Spurs got it done when it mattered most, even if they lost a game 7 at home the next season, while the Mavericks still haven't been able to get it done when it mattered most.
As for the rankings, after the discussions around here for the last 2-3 weeks, I'm surprised the Spurs are even in the Top 20 of anyone who's objective.