That was a response to @Mainline421's comment about giving (presumably all) through tickets break of journey validity. I assumed that the TfL cut from a 'maltese cross' ticket is less than that for a full zone one Travelcard where multiple journeys could be expected. A through ticket with a connecting TfL need only be priced for a single passtbrpugh validity. A passenger expecting to do a bit of shopping maybe also meeting somebody for lunch before continuing their journey would find a full zone 1 ticket more appropriate.Err, how so? If you're breaking your journey, you'd pass through a barrier line and thus it would be evident from the magstripe/smartcard data where you did that.
Really, it's no different to any other stretch of line in terms of the "revenue risk" it presents.