Germany is not the United States. You cannot just take (right wing winner percentage) minus (left wing loser percentage) and then declare that Merkel won a decisive mandate. The reality is that the CDU had their worst showing since World War II. The SPD is in even more trouble, but German politics are not a two-party affair, so this is not necessarily cause for unchecked celebration among the CDU.

Agreed. If anything, the FDP was the real winner of this election (along with smaller parties such as the Pirate Party, who managed to get onto the map). Both of the parties in the Grand Coalition lost ground, though the CDU lost less than the SDP as you mentioned. I think Germany's voters demonstrated their loss of confidence in either of the larger parties in this last election by submitting something of a protest vote.