20driver:
To my knowledge, the business-class-only services from DUS to the U.S. were originally offered to meet a high demand from local business travellers who did not want to go through FRA on their way across the Atlantic. Apparently the ratio of prospective business travellers to prospective cattle class pax living in the highly populated and industrialised Dusseldorf area was larger than than the corresponding seat distribution on regular wide-body ac's. Therefore it made sense to offer an additional "business only" flight.
In my personal opinion, I would prefer sitting on the top floor of a conventional wide-body aircraft. It might be irrational thinking, but larger aircraft simply feel safer to me, especially on long-haul trips. But I haven't made "zed3"s A319 experience yet, so I cannot really say anything at this point.