I have come across quite a few instance of 这回事(儿) instead of 这件事 - is there is a real difference between these or is it just a syntactical preference of the speaker?
 (measure) time (as used to indicate number of occurrence)
 (measure) piece (as used for happenings or events)
回 is a measure word for event or occurrence ; 这回事 means "this (piece of) event" or "this (time of) occurrence"
Different between 回 and 件 as measure word is:
回 measure specific course of events (how many times it happens)
件 measure event as an unit (how many of it exists)
就是这一回事 = it is this occurrence
當沒有这回事 = pretend there is no such occurrence
就是这一件事 = It is this event
當沒有这件事 = pretend this event doesn't exist
We also say 这回战斗(This battle) or 这回会谈(this discussion) ; but not 这件战斗 or 这件会谈.