This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
You are right that in this particular case a single element could be enough.
However it is a known convention to have a common root to all inner elements. So even though with one element it is not really helpful, it is still used. It also makes the SOAP more readable as the wrapper element name is based on the method name.
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