I've never met anyone who built a laptop from parts, so maybe you're comparing a desktop to a laptop. Building a desktop from parts is only useful if you can afford to spend the time debugging hardware or software when it's not stable. These days I need to use my computer for work, so it's not acceptable any more to spend 10 hours figuring out which top of the line part is failing so I can return it for warranty replacement. If I ever got another PC, I'd get a Dell. They're not the fastest or cheapest, but at least I know the network card isn't interfere with the video card in some unforeseen way because they've been well tested together before purchase.
On the OS end, there wasn't really such a thing as a power user in the 80s. To do anything remotely interesting, you need to do some heavy reading of Inside Macintosh, know assembly, and how to use Macsbug. Alternately, you could install someone else's hack, but sometimes these did the near impossible and made the OS even less stable. You couldn't even select a custom paper size in the Apple Writer print dialog, you had to pick from one of 5 or so. These days, there are a number of shells and scripting languages installed out of the box and a pretty nice terminal.