He's dumb? Far from it, he's managed to advertise himself very well, managed to get contacts within the industry, get sponsored by Lucozade and Razer (not entirely sure on that but they send him gaming gear and laptops). With the amount he is making why would he need to even bother building his own machine? I'm pretty sure he would have got a hefty discount or what not from the computer company as it's free advertising for them.
Making it on YouTube isn't all about video content, you need the personality. Although I don't really like his videos but I can see why he is so successful.