there are many much more blatant examples of such rip-offs in many kinds of media, including video games and movies

<cough>Tetris</cough>

Have you played GTA III or Vice City? You pretty much get Crazy Taxi thrown in for free as you can hop in a taxi and press a button and do the same thing. Granted I think Crazy Taxi is more fun in that respect b/c the driving is less realistic. None the less, the same "plot" is still there.

Then you have movies. "Last Man Standing" is a plot-line rip from "A Fistful of Dollars" which is a remake of "Yojimbo". But who's ever heard of "Yojimbo"? "A Fistful of Dollars" is (unfortunatly) becoming an unheard of movie as well. So is it ok to rip-off if your ripping from an old subject? What about all the movies that are take-offs of Shakespere plays?

Truthfuly, though it would never hold up in court, I think plagiarism (in this sense, not the accademic) can be summed up as "You know it when you see it". So in that sense, do I think that Simpsons: Road Rage is plagiarism? No, if people want to play Crazy Taxi they will buy Crazy Taxi.