Terrence Zdunich (one of the creators of REPO!) wrote a long, but interesting blog on his website about this.
He consulted a bunch of entertainment lawyers and they all told him the same thing: ideas are not copywrited. That means that Repo Men has to have whole chunks of dialogue or text lifted straight out of REPO! for them to be able to take any action. As it is, they cannot do anything just because Repo Men clearly has a similar idea.
Further, Terrence himself admits that, beyond the overall concept (which, you'll remember, is not copywritable), there isn't much in common between the two films. For one thing, Repo Men isn't a musical.
Nothing matters but knowing nothing matters. ~ Wicked
Everything in life is only for now. ~ Avenue Q
There is no future, there is no past. I live this moment as my last. ~ Rent
"He's a tramp, but I love him."