I do not believe you understand what I am saying about market fragmentation. As I alluded to above, until the early 80s, to get to Europe from the US you generally had to fly through BOS, JFK or one of the other few Atlantic gateways and the market was dominated by 747s, DC10s and L1011s. With increased range twins and more routes authorized (technology and deregulation) the market shifted dramatically to 767s and A310s (now including 777s and A330s) with nonstop routes to more and more US cities. A few carriers even are using 757s now! As a result, there are some 747s over the Atlantic, but they are in the minority. This is not some example of "strategies that come and go" as you mentioned, but is a trend that has been industry-wide over the last twenty years.
There will be some carriers that will use the A3XX on some of the very high density North Atlantic routes at peak times, but the last thing a carrier in business to make money wants to do is to fly empty seats. You state that "crossing the Atlantic on an A3xx in economy class is substantially cheaper than doing so in a 767 economy class." This is only true if every seat is full. If the A3XX seats are not full, then the 767, A330 and 777 become much cheaper to operate.
You also state that "A3xx business class will have fully reclining seats, which are a boon on overnight flights." This is a carrier preference and could be put into the current planes flying over the Atlantic. Seats and pitch are determined by the carrier. The greater the pitch, the fewer the seats and the more you must charge for each seat. That is true of every plane.
You also state that, "one reason smaller twins (widebodies twins) have become popular over the pond is that they haven't been essentially costlier to fly on than 747. A3xx will give cheap tickets, and for most passengers that's a very important point." I agree wholeheartedly that most passengers find the cost of their ticket important. At the same time, most passengers will pay a little more to fly nonstop instead of changing planes at BOS or JFK. The reason that the twins are flying over the Atlantic is that they are substantially cheaper to fly on these routes and do provide the cheapest seats based on the going load factors. The market (load factor) drives which plane is utilized on a given route. If your market averages 200 passengers a flight, which is cheaper to fly, a 767 or 747? Empty seats are not just lost revenue, they are additional and unwanted cost in a highly competitive environment.
I agree with your point that "ticket price, unlike some people seem to think, does impact on business travel as well." [See my point above. The twins provide cheaper seats in a fragmented market.] I have respectifully have to disagree with your comment "that secretaries don't type memos anymore, they spend a lot of time negotiating with travel bureaus to determine the cheapest way to travel for their colleagues." In most medium and large companies, the travel discounts have been negotiated and contracts signed with specific carriers. The same companies then either have inhouse travel agencies or contracts with outside agencies to monitor this and provided advice.
You're coming up with roughly the same numbers that I came up with for the A3XX. I do not disagree. My point is that this is not enough to even get close to break-even. What I'm trying to say is that I believe that the market is shifting to the smaller jets as the smaller wide-body twins (767, 330 & 777) as well as the 340 will command a much bigger market.
The reason 747 sales have been sliding is because it has too many seats for most markets, not because it is based on an older design. If the demand for seats was there, the sales would have been there. It has had no competitor so the slow sales reflect a decline in the market, not the plane.