Endless upgrades on NW had a lot more to do with the economics of the air travel industry at the time than with NW's particular upgrade policy. They had an F product that was not really worth paying for, and they also charged insane fares to book it, mostly relying on a very small group of corporate executives with F travel in their contracts to make some money off of the product. It was easily at least $2K for a mid-con sub 3 hour trip in F. Today those same flights on DL are usually under $1K when purchased at least a few weeks in advance. So I totally get why some are nostalgic for lots of free upgrades, but I think for most pax the current set up of having fares that are actually somewhat reasonable and within reach of many more people is more customer friendly.