I understand the similarities between the Angel and DeWitt twists. Although, I'm not sure if that's necessarily a bad thing. Very few shows have plots that are original anymore. I can't blame Joss for reusing SOME ideas. Unlike JJ Abrams.
JJ Abrams and his three shows: LOST, Fringe, and Alias. In all three shows there are the following similarities:
Main Characters as kids: LOST- All the passengers were visited as kids by Jacob, therefore being destined to be passengers on the same flight. Fringe - Olivia and other kids were experminted on as kids to be superweapons and fight the upcoming war between the two parallel worlds. Alias - Sidney Bristow and other agents were programmed and trained as kids to grow up and be super agents.
Doppelgangers: LOST - John Lock as the evil Jacob. Fringe - Olivia's friend, Agent Francis, has an evil clone. Alias- Sidney's best friend also has an evil clone.
Parallel Universes/Realties: All three shows deal with different and/or parallel realities.
See? Yet LOST still remains one of the best shows on air even though it borrows a lot of its plot devices from Abrams' previous show Alias.