No it's pegged to USD because it is backed by BTSX. BTSX does have value. It's an experiment, but it might just work. Perhaps this guy can explain how it works a little better than I have:
The only way a dollar peg can work is when there exists an entity (it doesn't matter what it is, it can even be an alien civilization) with very big amount of dollars, ideally infinite. When the pegged currency gets too cheap it has to spend dollars to maintain the peg.
There's no long-term reason for anyone to spend their dollars to maintain bitusd peg.
The short-term reason is a modified pyramid scheme: as long as the cost of maintaining a peg is less than the influx of new money from people buying into btsx because of currently working usd peg (and perhaps others), it will be maintained by major btsx holders.
http://bitcoinist.net/bitsharesx-i-join-the-grand-experiment...