Yawn. Just more extrapolating trends too far. Sure, when iCrap caught on, CD sales took a nose dive, but I still encounter CDs almost every day. They still fill a functional niche, and I suspect we'll still find CD-Rs on sale at Big Box for a long time. They're a cheap, portable way to physically transport a chunk data—especially audio. No, I'm not burning hundreds at a time, but when I need one, it's the best tool for the job. Contrast this to a floppy, which was totally unreliable, low capacity and utterly replaced by flash drives because of their superiority in almost every way.
Sure, we're probably headed for a world where a lot fewer people are buying 4GHz desktops with 8gb ram, and, sure, lots of people will herd happily into walled gardens, because they don't care or don't know better. There are people who only ever used their PC for facebook et al., hell, they probably already swapped it for a mobile device.
The thing we can't ever lose sight of is that consumer spending drives this industry. As long as people are willing to spend money for something, someone will be there to accept that money. Just ask the millions of PC gamers out there when they will trade their uber PC for a tablet. Just because something becomes less commonplace and more specialized doesn't mean it's just going to disappear. FUD.