The 2002 Spurs weren't a great champion either. And you notice they didn't repeat themselves.
I've watched Great teams (notice the big "G") play over the years, the Lakers, the Celtics, the old Bad Boy Pistons, Da Bulls -- teams that you DID pee your pants before playing because you had no idea how you could possibly beat them -- and this Piston crew is not remotely on that level. They have a short bench, problems scoring, and not a single historically great player on the roster (a first since the 70s I think). They're a great (notice the little "g") team, or at least were for half a season last year. Before that they were merely good. This year they've merely been good. They could win another title, and if everybody in their way collapses again I'm sure they're capable of pulling it off. But just as last year, they are only one among a pack of teams with a legit shot.
P.S. Discounting injuries is a cop out -- injuries are part of the game, but they absolutely factor in when you're trying to figure out who has the better team.