(and no couriers available to fall back on)
Luckily, they have plenty of *general purpose* organic units to fall back on, which, while less efficient than the tube network, can quickly transport the physical objects. Just because no one has "courier" in their job description, doesn't mean there are no available couriers.
Apple charges me around $100 each year to upgrade my G4 Mac from 10.3 to 10.4 to 10.5, whereas Microsoft charged me *nothing* to upgrade from XP to XP-SP1 to SP2 to SP3
That is hardly true. Upgrades once a year? 10.3 had a 1.5 year lifespan, 10.4 lasted almost 2.5 years, and 10.5 is nearing it's 2 year mark as well. Plus, the soon-to-come upgrade to 10.6 is only 29 bucks. Also, Windows service packs are minor updates, mostly for bugfixes and consolidated security patches; Apple doesn't charge for these minor updates either. All the OS X point upgrades (10.3, 10.4, 10.5) were *major* upgrades, packed with new features.
Over the last seven years using Wintel OS has been free, where using Apple's OS has been costly.
In other words, over the last seven years, Windows has not released any new features. And you're ignoring Vista, which you apparently were not forced to upgrade to; Interestingly, you weren't forced to upgrade to 10.3, 10.4 or 10.5, either. You always have the option not to buy; if you don't think the feature set of a particular release is big enough, wait for the next one, and you get double the features for the same price.
1 Sagan = Billions & Billions