No, that part wasn't tongue in cheek! I don't see any particular problem, its a general thing from all crews with regards omitting readbacks. In fact, a little story of the reverse scenario:
Long ago I was working a certain sector, busy in and out, with a request for a military C130 (RAF) to cross.
RFR1431 : RFR1431 with you, maintaining FL150, direct Dover**********************
Frequency then stayed open. I swear I could hear him unwrapping his sandwiches. Panic stations ensued; loads of co-ordination to get all Heathrow inbounds late descent, and to arrange 'headings to miss' for the outbounds.
Finally, frequency goes quiet. By this time, RFR 1431 left my airspace. I had to risk talking to him....
Radar: RFR 1431 you have been blocking the frequency for the last five minutes. DO NOT TRANSMIT, I SAY AGAIN, DO NOT TRANSMIT! Listen out on London 134.9.
RFR 1431: Roger London. Do not transmit, and listen ou... oh.. sorry.