I get the sense that PG wrote the essays and that book so they could be read many years in the future. Call it a decade for the timely ones, and much more than that for the rest. A few of the updates would be along the lines of "This needs to change from the future tense." For example, this brief review of the iPhone from 2001:
With Web-based software, most users won't have to think about anything except the applications they use. All the messy, changing stuff will be sitting on a server somewhere, maintained by the kind of people who are good at that kind of thing. And so you won't ordinarily need a computer, per se, to use software. All you'll need will be something with a keyboard, a screen, and a Web browser. Maybe it will have wireless Internet access. Maybe it will also be your cell phone. Whatever it is, it will be consumer electronics: something that costs about $200, and that people choose mostly based on how the case looks. You'll pay more for Internet services than you do for the hardware, just as you do now with telephones.