parsing a large XML in java can be a hog (Score 1)

Yes, potentially if they are parsing the XML into a full DOM tree, this could potentially take MASSIVE ammounts of memory. If you read up on the DOM parser for java. There are clearly many benifits of parsing an xml document into a DOM tree structurally and whatnot, but practically, at this point, if your document is large its just not viable memory wise. I don't know if this is what OO does, but its just a possible explaination.