I'm really surprised it has been the Washington Post that was so instrumental in destroying Rolling Stone's story. Has Sabrina Rubin Erdely made any public comment since this all fell apart? Seems she's pretty much been in hiding. Can't say I blame her.
It’s basically a local story for the Washington Post. UVa is maybe 90 minutes away from DC. Many Post reporters and their children are alumni, students, or future students.
the clue to why the Washington Post investigated the story is that it was not their political or national staff who did so, but the lowly reporters who cover local news. Those reporters were familiar with the University and had contacts to help them find out what really happened.