2000, Democrats: "We wuz robbed!"I think the issue is a more general avoidance by liberals and the left of any uncomfortable introspection. Thus, liberals would not look inside for what why they lost elections. Similarly but on the left, Karl Marx wrote endlessly on the supposed faults of capitalism but never examined critically his ideas of communism (Just how was his communist government supposed to 'wither' away?).
2002, Democrats: "We wuz robbed again!"
2004, Democrats: "We wuz robbed yet again!"
2006, Republicans: "Bummer. Oh, well, we'll do better next time."
Note that right-wing pundits and bloggers don't seem to be fixating on voter fraud, despite documented evidence that the Democrats have been doing that kind of thing? Note that Republican candidates who lost very narrowly gave in gracefully, without demanding recounts or resorting to the courts? Why the difference?
I think it's the basic Democrat culture of entitlement showing through. Democrats were angry in 2000, 2002, and 2004 because they felt that they deserved to win. Republicans don't feel that anyone deserves anything. They believe that all rewards have to be earned.
There's another way of looking at this. In 2000, 2002, and 2004, Democrats explained their defeat by looking to see what the Republicans had done to inflict defeat on the Democrats. In 2006, the Republicans seem to be explaining their defeat by loo king for all the ways they themselves loused up. The Democrats are showing their investment in the cult of the victim. They didn't lose because of any fault or failure of their own; they lost because of the nefarious acts of villainous Republicans.
On some larger levels, they will introspect endlessly: Democrats obsess on foreign policy issues like "why they hate us?" However, they obsess on this only in ways that leave liberals as the innocent victims of the wrong-headed policies of others. An example would be Sen. Murray's (D-Wa) famous theory that Islamic fundamentalists hate the US because the US has not spent enough money on foreign aid to build daycare centers in Islamic countries.