who says dl's coach service internationally is far inferior to that of co? i just flew to rome on co, and i had the most inedible meals i've ever experienced. i think you're drawing distinctions that don't really exist. the only advantages co has vs dl is they fly 777 on some routes, and they may have a more junior(therefore possibly more eager in-flight crew). otherwise, dl has traditionally offered the following;

1. better pricing
2. a longer period of availabity for purchase at lower fares (sometimes even day of vs co at least 3 days)
3. more routing options via code-shares with its partners (dl-af code shares to ssecondary european cities are much more affordable and extensive than co-af routes)

cuisine, in-flight entertainment, beverage service are quite similar. passable but in no way stellar.

as many people have said, the differences lie in upgrades. co's domestic are unlimited vs dl's accumulated(at least until you're platinum). dl gives systemwides(good on some int'l fares) vs co which only come from miles. by the way, if you get up to dl platinum you get your crc membership included, rather than buying a pres club mem from co.