Statecraft plays two roles in Zedruu decks. The first is the one you would expect from what the card read. basically, your creatures deal no combat damage, but other creatures don't deal combat damage to them either. The advantage of this is that your creatures can block mostly anything. It can even get around creatures with death touch since death touch requires at least one damage be dealt for it to kill the creature automatically.
What about in other decks? Some Kynaios and Tiro of Meletis lists that employ Zedruu have toyed with it. Really, the only other Commander to consistently try Statecraft is Phenax, God of Deception. His deck is based around creatures with high toughness in order to take advantage of the tap ability he gives them.
When Phenax is on board, he gives all creatures you control the ability to tap and make a player put the top X cards of his or her deck into the graveyard. since you're not looking to win by combat damage for the most part, you can rest assured that your creatures won't die in combat thanks to Statecraft.
Can Zedruu decks alone keep Statecraft a valuable card all by themselves? It's likely, considering how popular and good of a Commander she is. Statecraft isn't on the Reserved list however, so it could be reprinted in some future set or product. Still, if you're planning to play Zedruu in Commander at some point, Statecraft should definitely be in your list.