Let's go through it.
• If a big-time, Hollywood pretty boy with average intelligence can build his own PC, what does that have to do with becoming an audio/video engineer? Does building a PC help you understand choosing & setting up microphones? Does it give you an understanding of video compression? Does it give you a clue as to how to mix and master a song? The answer to all is, "No."
• That he's building the thing himself rather than just buying it or having a shop custom make it for him let's you know another thing: the guy has a lot of free time, he's cheap and rather stupid. He has more than enough cash to get the most powerful gaming PC made for him. The reason that gamers roll their own is because they can get the most bang for the buck making their own PC and they aren't millionaires. Cavill making his own and being so vain to make a video of it is pathetic on every level.
• Windows sucks! I have to use it on my Mac since I design web apps & sites and have to insure that they look the same on all browsers and platforms. Using Windows, after a few hours, makes me want to punch Bill Gates and Steve Balmer in the head... and take a shower. It's such a disgusting OS. If all you want to do is play games, though, it does offer the most titles.
• OK, the Idiot of Steel built his own PC. Did he show what his display(s) is? That's as important as the PC for conveying the gaming experience...possibly more. Since you didn't mention it, I'm assuming he didn't. If this was a car, he built the engine and transmission. You still have the body and suspension left. Of course, I doubt he could build a car or even change its oil.
• To show how lame Henry Cavill is, go to IMDB and look him up. He has no credits for anything, but acting. Even that imbecile Keanu Reeves has credits as a producer. If you get a producer or executive producer credit, that means that you have a bit of ownership in the production. You will keep getting paid royalties forever. Everyone seems to do that except for Henry Cavill.
So, given that fact and everything else I've mentioned, why is this dimwit or the act of building a PC so special?
Perhaps next, someone famous will make their own speaker cables, be stupid enough to put it on YouTube and you can offer up an item on that and ask why we aren't doing that as well.
Please do keep us up to date on movie stars doing mundane tasks in their down time.