Welcome to FT. Not quite sure which chart you found / are looking at, a link would have helped
If you're looking at
http://www.nwa.com/worldperks/travel/compan.shtml that refers to what classes you can upgrade with miles. Basically, on NW/DL, Elites are eligible for upgrades on any published, paid fare class. (On Delta, and NW in a few weeks after the merger, there's currently no upgrades on award reservations, though that is supposed to be put back in place in 2010. Certain unpublished fares, such as those booked by travel aggregators, may also not be upgradeable depending on the terms of the fare).
But basically, anything you buy on nwa.com, and basically anything you buy elsewhere (unless you're going through some consolidator -- and I don't mean expeida or orbitz, but some agent that instead books a giant block of tickets/seats to re-sell) you are eligible for an upgrade.
* Except if you use Delta's pay with miles. Sigh. This was not the case on NWA, with the Delta PWM program you don't get upgrades and you don't get miles either.