I certainly understand your point, but 25-plus years of "custom and usage" have made it hard to argue convincingly that purchasers don't know there's a click-wrap EULA. [EDIT: Enforceability of the EULA is usually predicated on the purchaser's having a reasonable period, usually 10 days or so, in which to return the software and get a refund if the EULA's terms aren't acceptable.]

The danger of the "Sold, not leased" approach is that vendors likely would stop offering such steep discounts for upgrades. Getting an upgrade would be be like buying a car: You want the new model, you pay the new-model price; and sure, by all means do whatever you like with your old model.