If you really want the XML you can get it. Basically, the CoreService response is actually in XML, and the WCF client will serialize/deserialize from/to XML, and what you can do is tell WCF that you want the XML for a given object.
Like this. (originally posted here)
SessionAwareCoreServiceClient client = new SessionAwareCoreServiceClient("wsHttp_2011");
ReadOptions readOptions = new ReadOptions();
IdentifiableObjectData tridionObject = client.Read("tcm:0-12-1", readOptions);
DataContractSerializer dcs = new DataContractSerializer(tridionObject.GetType());
using (MemoryStream ms = new MemoryStream())
ms.Position = 0;
XmlDocument document = new XmlDocument();
This will return R6 XML, it's not your father's R5 XML anymore, so you may have to play around with it for a while.