I could understand that, too, flyhigh. I just think that nobody really wants to merge with NW, leaving LCC and maybe CO (if it is left out of the dance, which is unlikely).
Look NW, DL and LCC have the least advantageous route networks of the so-called 6 legacy carriers, with DL the best positioned. I think that DL merging with NW would be DL choosing to go out of its way to make its recovery even more difficult by saddling itself with more secondary markets and relying on expensive connections for more leisure travel and opening itself up to MORE new low-cost competition. It seems that DL is trying to build in the mega markets, with its NYC promotion. DL should leverage its presence in NYC and ATL (that's got to be well over half its system). Furthermore, AMR could get some network benefit from SLC, even if it's not a sure-fire bet for the long term.
Obviously, AMR and DL have the most compatible fleets among any feasible combination of the big six.
Alternatively, I see DL and UA, for some of the same reasons above, except it would be a sure-fire dismantling of SLC, but retention of more NYC that would have to be pared in a combo with AMR. (However, part of the theory of an AMR and DL combination is that the merging partners might be able to convince the DOT that the massive removal of clogging RJs in and out of NYC airports would be worth some of the market skewing of such a combination..... In other words, Comair and American Eagle would pay a disproportionate burden in pulling down NE capacity in such a combination. )