I think we've had this discussion before, but yes, at times, especially "Arthur's Big Hit", D.W. practically got away with murder. It was very one-sided: Arthur told D.W. REPEATEDLY not to touch it, that it wasn't a toy, it was a model, and that it wasn't meant to be played with, and what does she do? As soon as he finishes it, she takes it, tries to fly it out the window, and breaks it. After he told her time and time again, not to touch it. And the thing that kills me the most is this exchange:

D.W.: And I'm sorry I broke your plane, but what kind of a airplane doesn't fly?
ARTHUR: A MODEL airplane?
D.W.: Well I didn't know that, I'm just a child, gimme a break!

Uh, she DID know that! Arthur TOLD her that, SEVERAL times, it's a MODEL airplane... and she doesn't need a break, she already got one when she barely (if even so) got punished for breaking it.

And likewise, with "Play it Again, D.W.", it really wasn't fair for their parents to punish Arthur simply for threatening to wreck D.W.'s CD, but not give her a talking to about her constantly playing it to the point of annoying her brother, until AFTER they took the CD by mistake, and returned it to her.