It's a cool use of 3D Printing; but couldn't just putting the victim's finger on the phone work?
If you would have read the article, it states that the body was too decayed. Another possibly scenario would be where the body hasn't been found yet and they find the phone in the victim's apartment, along side the road, etc... There are plenty of situations where you might have a prerecorded fingerprint but not a body.
Oh, and call me cynical but my guess is that one of the reasons it's being tried in this case is to set a precedence in a "safe" case so they can later use it against living people with a search warrant.