"If you're dumb enough to keep paying the enormous price for a new Mac every few years"
This is simply not true any more, although the persistence of the myth is a credit to Grungeware's advertising department -- probably the only part of the organization that's really good at their jobs.
Macs are not all that expensive unless you have to buy the cute little iMac in order to be hip. You can get a G4 PowerBook laptop for well under $1,000, or a G4 desktop machine for well under $2,000. Both are performance-competitive with current-generation quality-brand PC hardware unless you're a videogame junkie (in which case you probably have a PowerStation), or a top-end graphics professional (in which case you wouldn't be caught dead with a PC at any price).
The modest actual price differential is a classic case of "you get what you pay for." Contrary to your implication, as the personal computer consumer base continues to expand well beyond the circle of aficionados, they are increasingly LESS fascinated by the prospect of having to become software mechanics in order to get e-mail, read the news, balance their checkbook, and manage their music libraries.
It's true that Macs aren't upgradeable and if you want to be compatible with current applications you have to have current hardware. But the multi-faceted advantages of that far outweigh the disadvantage, which has only one dimension: dollars. Each generation of Mac hardware is designed from scratch, and each generation of Mac OS is built from the ground up to integrate with it.
The significance of this is twofold. Macs are not wheezing along on an architecture that has (barely and clumsily) evolved from a text-only, keyboard-only, monochrome, silent, unanimated, single-tasking, non-networked ancestor. And OS/X is not rife with as-yet unidentified security wormholes inherited from three versions ago, nor with the new defects that are inevitably introduced by the exasperated, cloogey upgrading of legacy code instead of building new software with state-of-the-art software development methodologies.
More than half of the Earth's population is not wired yet. They have no financial or emotional investment in existing IT to guide their purchasing decisions. I would imagine that the current dismal state of the PC/Windows-based "information infrastructure" is enough to make Macs very attractive to them.