I think that Boeing's strategy is very good:
B717: It's a plane for very short distances, and very cheap. But its passenger capacity is medium (not like SAAB or ATR planes). This is a new product, it haven't any competitors (SAAB, ATR is too small but A318/19/20/21 and 737 is medhaul planes (they are more expensive)). B717 is useful for medium density very short distances (Berlin-Warshaw).
B737: It's a medium passenger capacity plane for medium range distances. All airlines (except airlines which use all-Airbus strategy) have this planes (small airlines too). B737 is useful for medium density medium distances (Madrid-London).
B747: It's a huge longhaul plane with very big passenger capacity. All major airlines have it (airlines, which use all-Airbus strategy included!!!). It's the best Boeing's plane without competitors in all the world. Airbus didn't made any planes with very big passenger capacity like this. B747 is useful for transatlantic big density flights (Paris-Detroit).
B757: It's large passenger capacity medhaul plane. It's bigger than B737. In USA it is very popular, because all flights density in this country is big. In Europe most medhaul flights density are medium, and B737 is most useful here. B757 is useful on high density medhaul flights (Los Angeles-Dallas).
B767: It's large passenger capacity longhaul plane. Capacity is like B757, but it range is longer. It's smaller than 747 and most popullar transatlantic plane in large density (but smaller than 747) flights. All small countries airlines, which want to start the transatlantic flights, use it. This plane is cheaper than other Boeing's longhaul planes and it's very good for small airlines. B767 is useful for large density transatlantic flights (Warshaw-New York).
B777: It's large passenger capcity longhaul plane. You can compete it whith B767, but B777 is better. And more expensive too. It's more comfortable, and its range is bigger too. B777 is A340 competitor, but 777 is better. B777 is useful for large density transatlantic flights (Berlin-New York)