Hi,
CSV / TSV reports were historically made for the UI users / API users who wanted to display results directly to the users without much processing. So they included summary rows. XML reports were meant for developers who wanted to process the rows further, so we kept only the raw data rows in this report.
The reason why we support the skipReportHeader and skipColumnHeader headers is because many users prefer parsing a csv file instead of an XML file - not all programming languages have good support for XML parsing.
Unfortunately, I don't think there's a source I can link you to. You could either calculate the summary rows yourself, or switch to a reporting format that supports it. In case you need help figuring out how to calculate various summary rows, feel free to open a new thread on the forum.
Cheers,
Anash P. Oommen,
AdWords API Advisor.