I disagree. The Mainframe era is evolving, not ending. How many people still have and use a mainframe when they interact with their bank? PCs are filling a growing demand for an OS on a smaller form factor, but the traditional mainframe market is still alive and kicking, its just not "cool" anymore; it's seen as more of a utilitarian tool than a novelty at this point, whereas PCs currently retain the novelty factor, thus their pervasiveness at BigIronExpo.
Yup. I actually recall people making this argument back in those days. And they were right in a sense: big iron still exists in its niche, after all. Regardless, the PC revolution was still a massive shift — large enough to justify the rise of the PCs as heralding the demise of big iron.
I'm not entirely convinced things will pan out like this, but the thought still occurred to me.
Televisions, radios, cars, and home appliances are all devices that are harder to tinker with today than when they were first invented. Computer hardware, for the most part (outside of hobby kits) is all magic black boxes plugged into each other. Something wrong with your video card? There's not much you can do about it.
Luckily, the hobby/amateur market in computer hardware/software (and other hobbies, like cars) is still alive and kicking. IMO though, corporations seem to like taking steps to make that sort of work harder (e.g., utilizing encryption to ensure "blessed" hardware/software can only be used).
I've given some thought to this, and I don't think that it can mostly be blamed on the corporations. Sure, they're part of it, but I think the ever increasing complexity of technology is mostly what causes things to be harder to tinker on. There's far more to understand than in older technology, and it makes tinkering/hacking on things far more difficult.
It's kind of like classic cars vs cars today. Older cars were much more tinkerable/hackable/etc, but newer ones have certainly benefited from the increased complexity in the form of better gas mileage, safety, etc at the cost of hackability.
The demise of hackability is and will be due to DRM and the hardware equivalents (like impossible-to-find proprietary screwdrivers).