The Bundeshliga is a very difficult league (with arguably the best football played in Europe), with plenty of good sides and lots of good players even with the smallest clubs (Relegated FC Koln had Podolski last season!).
Beating Bayern Munich to the title two seasons in a row is a remarkable achievement, and incredibly hard to do.
I like Dortmund's transfer policy of selling a big name player, and getting several little known stars of the future with the money from the transfer.
Dont get me wrong. What Dortmund have done in 10 years or so is great and they should be viewed as a model for clubs on how to operate.
And I'm not saying beating Bayern twice and also in cups isn't hard. It would just be much harder if there were more clubs with Bayern's financial might in Bundesliga for Dortmund.